The latest version of the ADO.NET Entity Framwork Community Technology Preview has been released. You can get it at the Microsoft download site ADO.NET Entity Framework June 2007 CTP. This CTP contains updates to the ADO.NET Entity Framework since the Visual Studio Codename "Orcas" Beta 1 release, including changes in Object Services, Query, Entity Client, and the Entity Data Model Wizard in Visual Studio.
Some of the new features include IPOCO, detaching from long-running ObjectContext instances, multiple entity sets per type, support for referential integrity constraints, span support, transactions, serialization, no more default constructors in code-generated classes, improvements to stored procedure support, access to the underlying store connection, directory macros in the entity connection string to support hosted scenarios, native SQL read-only views, UNICODE support in Entity SQL, query plan caching, and canonical functions in Entity SQL.
The Entity Framework will not be shipping with Visual Studio 2008 "Orcas". The Entity Model Designer and Entity Framework will ship as an extension to Visual Studio 2008.
If you use it, be sure to follow the installation instructions. According to the ADO.NET Team Blog this particular CTP will work only on Visual Studio Web Developer Express. According to the blog, "This is a CTP and the only edition of Visual Studio that works for this release is Visual Web Developer Express. This means that you will only be able to author Web sites in Visual Studio. Nothing prevents you from building console applications or WinForms applications outside of Visual Studio and building them with MSBuild and a .NET Framework compiler, but you will not be able to work on those project types inside Visual Web Developer Express." However you can compile WinForms examples from the command line.
You can learn more about Entity Framework in the Entity Framework Overview. A Channel 9 video explains ADO.NET Entity Framework: What. How. Why. And an MSDN article ADO.NET Entity Framework Overview describes how it works and includes example code.