UI guidelines for Longhorn (called Aero). Longhorn Aero UI Sampler.
I just ran across this nice set of Longhorn UI related articles, officially titled Aero User Experience Guidelines: Sampler for PDC 2003. Links to the meat are under What's Inside? heading. Some good ideas, some questionable, but all good looking. I am starting to get a little sick of all the gradients though and the huge titlebar seem wasteful. I wonder what usability tests caused them to make the title bar much bigger?
[Don Park's Daily Habit] [via Marc's Voice]