Microsoft has introduced new features in .NET with their Service Pack 1 (SP1) release of .NET Framework 3.5 and Visual Studio 2008.
Most of the stuff included in the service pack releases is new features and functionality rather than bug fixes and updates to existing feature-set. For example, .NET Framework 3.5 SP1 adds a new concept called the .NET Framework Client Profile, which enables an application to be delivered with just what is needed to install and run the app, rather than the whole framework. This can reduce the size of installation files by 86.5 percent, according a Microsoft spokesperson. Other major features in .NET Framework 3.5 SP1 include a 20 to 45 percent improvement in Windows Presentation Foundation (WPF) applications and changes to the Windows Communication Foundation (WCF) to change the way data and services are accessed.
The changes in the Visual Studio 2008 SP1 and .NET Framework 3.5 SP1 are listed here.