I have been heads down into the PDC Longhorn bits. I am very excited by everything so far. I think XAML is going to be the best thing for user interface design to come along in a while. I like the ability to run the XAML files right in the browser, this is way cool. Here are a couple of Longhorn links to documentation.

http://longhorn.msdn.microsoft.com

http://msdn.microsoft.com/longhorn