Without a doubt, WPF is one of the coolest features of Vista. If you're a new Vista user and want to see an example of how WPF opens up new alternatives to UI, check out UniveRSS. This WPF app lets you explore your RSS feeds in a 3D space, mapping your feeds to rotating cubes. There is a grid view if you prefer old-school navigation. Best of all, the app is only a 364k download.