Sweet, there is an update Futures CTP. The download is over 50 MB, so I assume that there is documentation included with it.
Overview (from the MS download page):
The Microsoft ASP.NET Futures May 2007 (“Futures”) release
contains an early developer preview of features providing a wide range
of new functionality for both ASP.NET and Silverlight™. The
functionality in the Futures release includes early experimental
versions of features currently being considered for future versions of
ASP.NET and the .NET Framework. The Futures releases assume prior
knowledge of the core features of ASP.NET including the previous
ASP.NET AJAX Futures January CTP.
Features in this release include ASP.NET Silverlight server controls, new functionality for ASP.NET AJAX Extensions, dynamic data controls, enhancements to dynamic languages, and more.