I have mentioned before that a CLR update is due to be released this summer.

Scott Guthrie just announced that a beta is now available. On the CLR, he says:

.NET 3.5 SP1 includes significant performance improvements to the CLR that enable much faster application startup times - in particular with "cold start" scenarios (where no .NET application is already running).  Much of these gains were achieved by changing the layout of blocks within CLR NGEN images, and by significantly optimizing disk IO access patterns.  We also made some nice optimizations to our JIT code generator that allow much better inlining of methods that utilize structs.

We are today measuring up to 40% faster application startup improvements for large .NET client applications with SP1 installed.  These optimizations also have the nice side-effect of improving ASP.NET application request per second throughput by up to 10% in some cases.

It's not just an update to the CLR though, it's a significant service pack to both the .NET Framework and Visual Studio 2008. Another novelty I'm definitely going to take a look at is Linq to Entities:

.NET 3.5 SP1 includes the new ADO.NET Entity Framework, which allows developers to define a higher-level Entity Data Model over their relational data, and then program in terms of this model.  Concepts like inheritance, complex types and relationships (including M:M support) can be modeled using it.

The ADO.NET Entity Framework and the VS 2008 Entity Framework Designer both support a pluggable provider model that allows them to be used with any database (including Oracle, DB2, MySql, PostgreSQL, SQLite, VistaDB, Informix, Sybase, and others).

Developers can then use LINQ and LINQ to Entities to query, manipulate, and update these entity objects.