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EntityFramework (ORM) object names and domain model names - how to avoid duplicates?

Let's say I have a project where I use Entity Framework, but I want to use my own classes instead of the EF classes.
Reasons for using my own classes:
Easy to add properties in code
Easy to derive and inherit
Less binding to the database
Now, my database has table names like User and Conference.
However, In my domain project, I also call my files User.cs and Conference.cs.
That means I suddenly have two objects with the same naming, which is usually very annoying to work with, because you have to use namespaces all the time to know the difference.
My question is how to solve this problem?
My ideas:
Prefix all database tables with 'db'. I usually do this, but in this case, I cannot change the database
Prefix or postfix all C# classes with "Poco" or something similar
I just don't like any of my ideas.
How do you usually do this?

It's difficult to tell without more background but it sounds like you are using the Entity Framework designer to generate EF classes. This is known as the "Model First" workflow. Have you considered using the Code First / Code Only workflow? When doing code first you can have POCO classes that have no knowledge of the database, EF, or data annotations. The mapping between the database and your POCOs can be done externally in the the DBContext or in EntityTypeConfiguration classes.
You should be able to achieve your goal of decoupling from EF with just one set of objects via code first.

To extend the above answer, the database table name User (or Users as many DB designers prefer) is the identifier for the persistence store for the object User that's defined in your code file User.cs. None of these identifiers share the same space, so there should be no confusion. Indeed, they are named similarly to create a loose coupling across spaces (data store, code, development environment) so you can maintain sanity and others can read your code.

Adding functionality to my Entity Framework POCO classes

I've built a web application with Entity Framework using POCO.
I'm using these POCO classes as my business objects and not just for persisting data which works fine until...
Now I need to add some logic into these classes to do thing like total up sales, order lines, etc.
Should I add methods to my POCO classes to enable this functionality or leave them purely for persisting data and create some kind of 'processor' whereby I pass in the business objects and get the values I require out.
Is there a best practice for this?

What is the architectural design you are using or want to use?
For example, if these are your domain entities, you should put as much as possible logic in them. If they are merely data containers and you don't have a real architecture in place, your logic would probably in some business component.
So if you provide your question with some more details, we can help you better.

DAL: DataContext principles understanding

Not sure if there's a "offical" name, but by DataContext I mean an object which transparently maintains objects' state, providing change tracking, statement-of-work functionality, concurrency and probably many other useful features. (In Entity Framework it's ObjectContext, in NHibernate - ISession).
Eventually I've come to an idea that something like that should be implemented in my application (it uses mongodb as back-end, and mongodb's partial updates are fine when we're able to track a certain property change).
So actually, I've got several questions on this subject
Could anyone formulate requirements to DataContext? - what's your understanding of it's tasks and responsibilities? (The most relevant I've managed to find is Esposito's book, but unfortunately that's at about msdn samples level).
What would you suggest for changes tracking implementation? (In simplest way it's possible to track changes "manually" in entities, but requires coding and mixes dal with business logic, so I mostly interested in "automatic" way, keeping entities more poco).
Is there way to utilize some existing solution? (I hoped nhibernate infrastructure would allow plugging-in custom module to work with mongo behind the scene, but not sure if it allows working with non-sql dbs at all).

The DataContext (ObjectContext or DbContext in EF) is nothing else than an implementation of the Unit of Work (UoW)/Repository pattern.
I suggest you Fowler's book on Patterns of Enterprise Application Architecture in which he outlines the implementation of several persistency patterns. That might be a help in implementing your own solution.
A DataContext basically needs to fullfil the job of a UoW. It needs to handle the reading and management of objects that are involved in a given lifecycle (i.e. HTTP request), s.t. there are no two objects in memory that represent the same record on the DB. Moreover it needs to provide some change tracking for performing partial updates to the DB (as you already mentioned).
To what regards change tracking, I fully agree that polluting properties with change events etc is bad. One of the recent templates introduced in EF4.1 uses Proxies to handle that and to give the possibility to have plain POCOs.

Answer to quetion 2: To make POCO classes work, you will need to generate code at run-time, possibly using System.Reflection.
If you analyse EntityFramework, you will see that it requires virtual properties to do change-tracking... that is because it needs to create a generated class at run-time, that overrides each property, and then adds code to tell the DataContext when someone changes that property.
EntityFramework also generates code to initialize collections, so that when someone try to do operations like Add and Remove, the collection object itself knows what to do.

Rich domain model with ORM

I seem to be missing something and extensive use of google didn't help to improve my understanding...
Here is my problem:
I like to create my domain model in a persistence ignorant manner, for example:
I don't want to add virtual if I don't need it otherwise.
I don't like to add a default constructor, because I like my objects to always be fully constructed. Furthermore, the need for a default constructor is problematic in the context of dependency injection.
I don't want to use overly complicated mappings, because my domain model uses interfaces or other constructs not readily supported by the ORM.
One solution to this would be to have separate domain objects and data entities. Retrieval of the constructed domain objects could easily be solved using the repository pattern and building the domain object from the data entity returned by the ORM. Using AutoMapper, this would be trivial and not too much code overhead.
But I have one big problem with this approach: It seems that I can't really support lazy loading without writing code for it myself. Additionally, I would have quite a lot of classes for the same "thing", especially in the extended context of WCF and UI:
Data entity (mapped to the ORM)
Domain model
WCF DTO
View model
So, my question is: What am I missing? How is this problem generally solved?
UPDATE:
The answers so far suggest what I already feared: It looks like I have two options:
Make compromises on the domain model to match the prerequisites of the ORM and thus have a domain model the ORM leaks into
Create a lot of additional code
UPDATE:
In addition to the accepted answer, please see my answer for concrete information on how I solved those problems for me.

I would question that matching the prereqs of an ORM is necessarily "making compromises". However, some of these are fair points from the standpoint of a highly SOLID, loosely-coupled architecture.
An ORM framework exists for one sole reason; to take a domain model implemented by you, and persist it into a similar DB structure, without you having to implement a large number of bug-prone, near-impossible-to-unit-test SQL strings or stored procedures. They also easily implement concepts like lazy-loading; hydrating an object at the last minute before that object is needed, instead of building a large object graph yourself.
If you want stored procs, or have them and need to use them (whether you want to or not), most ORMs are not the right tool for the job. If you have a very complex domain structure such that the ORM cannot map the relationship between a field and its data source, I would seriously question why you are using that domain and that data source. And if you want 100% POCO objects, with no knowledge of the persistence mechanism behind, then you will likely end up doing an end run around most of the power of an ORM, because if the domain doesn't have virtual members or child collections that can be replaced with proxies, then you are forced to eager-load the entire object graph (which may well be impossible if you have a massive interlinked object graph).
While ORMs do require some knowledge in the domain of the persistence mechanism in terms of domain design, an ORM still results in much more SOLID designs, IMO. Without an ORM, these are your options:
Roll your own Repository that contains a method to produce and persist every type of "top-level" object in your domain (a "God Object" anti-pattern)
Create DAOs that each work on a different object type. These types require you to hard-code the get and set between ADO DataReaders and your objects; in the average case a mapping greatly simplifies the process. The DAOs also have to know about each other; to persist an Invoice you need the DAO for the Invoice, which needs a DAO for the InvoiceLine, Customer and GeneralLedger objects as well. And, there must be a common, abstracted transaction control mechanism built into all of this.
Set up an ActiveRecord pattern where objects persist themselves (and put even more knowledge about the persistence mechanism into your domain)
Overall, the second option is the most SOLID, but more often than not it turns into a beast-and-two-thirds to maintain, especially when dealing with a domain containing backreferences and circular references. For instance, for fast retrieval and/or traversal, an InvoiceLineDetail record (perhaps containing shipping notes or tax information) might refer directly to the Invoice as well as the InvoiceLine to which it belongs. That creates a 3-node circular reference that requires either an O(n^2) algorithm to detect that the object has been handled already, or hard-coded logic concerning a "cascade" behavior for the backreference. I've had to implement "graph walkers" before; trust me, you DO NOT WANT to do this if there is ANY other way of doing the job.
So, in conclusion, my opinion is that ORMs are the least of all evils given a sufficiently complex domain. They encapsulate much of what is not SOLID about persistence mechanisms, and reduce knowledge of the domain about its persistence to very high-level implementation details that break down to simple rules ("all domain objects must have all their public members marked virtual").

In short - it is not solved
(here goes additional useless characters to post my awesome answer)

All good points.
I don't have an answer (but the comment got too long when I decided to add something about stored procs) except to say my philosophy seems to be identical to yours and I code or code generate.
Things like partial classes make this a lot easier than it used to be in the early .NET days. But ORMs (as a distinct "thing" as opposed to something that just gets done in getting to and from the database) still require a LOT of compromises and they are, frankly, too leaky of an abstraction for me. And I'm not big on having a lot of dupe classes because my designs tend to have a very long life and change a lot over the years (decades, even).
As far as the database side, stored procs are a necessity in my view. I know that ORMs support them, but the tendency is not to do so by most ORM users and that is a huge negative for me - because they talk about a best practice and then they couple to a table-based design even if it is created from a code-first model. Seems to me they should look at an object datastore if they don't want to use a relational database in a way which utilizes its strengths. I believe in Code AND Database first - i.e. model the database and the object model simultaneously back and forth and then work inwards from both ends. I'm going to lay it out right here:
If you let your developers code ORM against your tables, your app is going to have problems being able to live for years. Tables need to change. More and more people are going to want to knock up against those entities, and now they all are using an ORM generated from tables. And you are going to want to refactor your tables over time. In addition, only stored procedures are going to give you any kind of usable role-based manageability without dealing with every tabl on a per-column GRANT basis - which is super-painful. If you program well in OO, you have to understand the benefits of controlled coupling. That's all stored procedures are - USE THEM so your database has a well-defined interface. Or don't use a relational database if you just want a "dumb" datastore.

Have you looked at the Entity Framework 4.1 Code First? IIRC, the domain objects are pure POCOs.

this what we did on our latest project, and it worked out pretty well
use EF 4.1 with virtual keywords for our business objects and have our own custom implementation of T4 template. Wrapping the ObjectContext behind an interface for repository style dataaccess.
using automapper to convert between Bo To DTO
using autoMapper to convert between ViewModel and DTO.
you would think that viewmodel and Dto and Business objects are same thing, and they might look same, but they have a very clear seperation in terms of concerns.
View Models are more about UI screen, DTO is more about the task you are accomplishing, and Business objects primarily concerned about the domain
There are some comprimises along the way, but if you want EF, then the benfits outweigh things that you give up

Over a year later, I have solved these problems for me now.
Using NHibernate, I am able to map fairly complex Domain Models to reasonable database designs that wouldn't make a DBA cringe.
Sometimes it is needed to create a new implementation of the IUserType interface so that NHibernate can correctly persist a custom type. Thanks to NHibernates extensible nature, that is no big deal.
I found no way to avoid adding virtual to my properties without loosing lazy loading. I still don't particularly like it, especially because of all the warnings from Code Analysis about virtual properties without derived classes overriding them, but out of pragmatism, I can now live with it.
For the default constructor I also found a solution I can live with. I add the constructors I need as public constructors and I add an obsolete protected constructor for NHibernate to use:
[Obsolete("This constructor exists because of NHibernate. Do not use.")]
protected DataExportForeignKey()
{
}

Entity Framework POCO Object Creation

we are currently using EF 4.1 and are thinking about a new alternative for our object model which is terrible. We do have POCOs in a sort of BL-Layer and above a GUI-Model with Objects wrapping the POCOs to offer BindingLists to the UI instead of the BL's IEnumerables.
We thought about deriving the UI-Model from the POCOs but I have no Idea how this would work with the EF instantiating the objects as it shouldn't know anything about the UI objects. Is there some way to move the instantiating process to factories or does anyone have an idea how to promote the object afterwards from base to derived type (which isn't really a good idea at all, is it?)
Any help, suggestions or comments would be highly appreciated.
Best regards
Gope

No it is not possible to move object instantiation to factories. Because of that deriving custom classes from your entities will not work because EF will not create those instances for you and you will also not be able to persist those instances because EF will not know how to map them.

The introduction of POCO support in EF4 was to allow the business objects to exist without extending objects in the EF (specifically EntityObject). I've worked on a number of systems now where the domain model is shared across all layers in the system and a repository patterns is used to handle object persistence. A number of teams use the concept of data transfer objects (DTO) to provide the UI with a lightweight object that the UI can work with (which also provides a certain degree of abstraction to the BLL from the UI).
Microsoft Spain recently published a document and sample application that talks about how to structure enterprise applications (http://microsoftnlayerapp.codeplex.com/) which might give you some ideas about how to structure things better.