Yesterday, the publishing process was completed for the online version of the XNA Game Studio 3.0 documentation.  You can access this documentation at http://msdn.microsoft.com/library/bb200104.aspx.

The documentation is also installed as a part of the XNA Game Studio 3.0 product if you would like to use the documentation on your computer without requiring access to the Internet.  You can launch the documentation by clicking on the Windows start menu, choosing All Programs, then XNA Game Studio 3.0, then XNA Game Studio Documentation.