MVC2, EF4, layers, STE and validation

Question

I see that most of people interested in EF4 are MVC developers. So; for a MVC2 medium application that implements DDD (Interfaces, Repositories, Services, Entities and IoC):

Do you recomend separating the different concerns in layers and using Self Tracking Entities? (here I know that ObjectChangeTracker is not being used but I don't find any template that creates only the graph)

Or it is preferable having all in the same project with the entities dependant on EF and validation based in DataAnnotations?

I would prefer having layers. And validation like this. We have always developed separating bussines and persistence.

I have also seen performance comparisions where EF Object Entities are worse than using POCOs.