One of the nicest features of EF 4.0 is POCO support, which makes possible to do persistence ignorance with Entity Framework. Another great feature, which I was expecting to be released as part of EF 4.0 is support for Self-Tracking Entities. Self Tracking Entities are domain classes that do not have any dependency on Entity Framework but include mechanisms that allow them to track changes regardless of where those changes are done. This allows you to build N-tier solutions with EF 4.0 in a pretty easy way.
In order to generate POCO classes and Self Tracking Entities Microsoft's plan is to ship T4 Templates, which allow you to completely replace EF code generation with custom code.
Now a couple of weeks ago the EF Team announced that this functionality (Self-Tracking Entities and T4 Templates for POCO and Self-Tracking Entities) is not scheduled to be part of the .NET Framework 4.0 and therefore it is part of the new Entity Framework Feature CTP 1 Pack and as such the team is looking for lots of feedback on these components.
Obviously it would has been nice if it came as part of the .NET 4 release; on the other side I'm pretty sure that the Team is really committed to deliver a high quality EF Feature Pack at the time .NET 4 will be in RTM and moreover it contains also other extensions like Code Only (see below).
More on EF Feature CTP 1 can be found at the ADO.NET Team Blog: