As I recently have experienced a few days ago the first beta version of the service pack 1 for Visual Studio 2008 and .NET Framework 3.5 have been released.

The release of the final version is announced for summer.

This servicing updates provide a roll-up of bug fixes and performance improvements.
Furthermore, additions and enhancements that make building .NET applications have become better.

The parts that provide development with C++/MFC won’t have many new features but C# development is said to be improved.

In any case you’d be aware of:

• Users that have Windows Vista should have SP1 for Vista installed before upgrading the .NET 3.5 Framework with SP1.
• Any users who still work with beta of Visual Studio 2008 (Codename Orcas I think) will get in trouble when trying to install the service pack. A detailed step-guide can be found here.
• There is a change in behavior in the .NET 3.5 SP1 beta that causes a problem with the shipping versions of Expression Blend (WYSIWYG-Editor für XAML). The recommented way to work around this issue is to download the recently updated version of Blend 2.5.

At least bear in mind “be careful - it’s still beta form”. The usage on critical system is not recommented yet.

Scott Guthrie (Corporate Vice President der Microsoft Developer Division) has done a great blog post that shows the improvments in detail.
It can be found here.

The Visual Studio SP1 Beta is quite extensive and includes support for SQL Server 2008, new ADO.NET features, improvements to the WPF designers, WCF templates for Silverlight projects, debugger support for the .NET Framework public symbols and source release, control improvements and Visual C++ improvements such as the Office 2007 Ribbon bar.