.NET 3.5 SP1 and VS 2008 SP1 provide a bunch of bug fixes,
performance improvements, and additional feature enhancements that make
building all types of .NET applications better. It will be a fully
compatible service pack release.
We plan to ship the final release of both .NET 3.5 SP1 and
VS 2008 SP1 this summer as free updates. You can download and use the
beta now here.
Hope this helps,