Last month, the MSDN team published a doc that's long been in the works -- a developer's introduction to some of the new APIs in Windows Vista.  The real meat is in the .chm file (self-extracting exe), with some sample code and detailed API info.

This is only a start, and it covers only a small portion of the new platform features in Vista, but it's a good place to start learning about how to make applications really light up on Vista.