Docs for .NET Framework 4 Beta 2, Windows Presentation Foundation (WPF), and Visual Studio 2010 Beta 2 are now available at MSDN. You can get information on installing the beta here.

Here are some of the latest updates to the WPF documentation that you might want to check out.

In addition, you might want to check out the new MSDN views - lightweight and scriptfree - that provide better performance while using the documentation.