 <p>It largely depends on your overall technology stack. If you're already set up with nHibernate and there's no external motivating factor (business reason, etc), then there's no true need to move over to EF4. However, if you're almost exclusively using the MS technology stack, then moving to EF4 will further that effort.</p> <p>That said, Spring.NET and nHibernate have a great, mature history of interoperability, and it's tough to fix what isn't broken. I'm in the process of building up a Domain Model using POCOs with EF4 and Spring.NET and can attest there are a lot of learning opportunities and instances of "OK, how am I going to do THAT?". But it's certainly doable and while there aren't many resources out there specifically of using EF4 and Spring.NET, there is good guidance in the general realm of EF4 and DDD.</p> <p>Dunno if that helped at all, but it's my two cents on the topic.</p>