The ADO.NET team details on its blog what has changed for LINQ to SQL with the release of Visual Studio 2008 and .NET 3.5 Service Pack 1 Beta:
Across the LINQ to SQL we have made numerous bug fixes, better SQL translation for queries comparing nullable columns in Visual Basic, and support both in the runtime and the designer for SQL Server 2008.
New SQL Server 2008 Support includes:
- Support for connecting to SQL Server 2008 databases in Server Explorer
- Drag & drop tables in SQL Server 2008 databases from Server Explorer
- Support for the following new types: Date, Time, DateTime2, DateTimeOffset, Filestream
The above is just for LINQ to SQL, but this service pack comes with lots and lots of updates and new features! The ADO.NET team also has a detailed list of what's new for Entity Framework, as well as a list of breaking changes for Entity Framework. The same kind of information can be found on the Astoria team's blog for ADO.NET Data Services (Astoria).
You can get a good overview of what's included in this service pack on Scott Guthrie's blog. There are way too many changes included to repeat them all here.
Note: Scott adds that "The debugger in VS 2008 SP1 has also been improved to provide more debugging support for evaluating LINQ expressions and viewing results at debug time. LINQ enabled data sources now have a "Results View" node show up within the debugger watch window. Expanding this node will evaluate a LINQ expression and allow you to examine the materialized objects it returns."