I'm really excited about the new Windows graphics subsystem, the Windows Presentation Foundation (insert WPF vs. Avalon joke here). I am teaching myself the new API by working on a sample application which is a simple card game. Maybe I'll post some screenshots and sample code here soon. Anyways, the ease of declaring an impressive yet flexible UI using XAML is surprising. Check out this great article on the Top 10 UI Development Breakthroughs made possible by the WPF.