I remember seeing some demos of "Avalon" (now dubbed the Windows Presentation Foundation) a while back and was impressed with how simple it is to build up the UI (using XAML), however Microsoft have just released a new video, that is very graphic, I think they were just using Notepad in the one I saw but this actually shows all the changes happening in real time in the little application they put together. Very impressive stuff, especially when they start throwing in videos and things.
Check this out. I've already been thinking about doing an "Avalon" front end for my websites, the stuff you can do is just amazing.
PS Avalon = cool name, will take me a while to get used to Windows Presentation Foundation.