Family.Show app shows of WPF, source code is available
Saving the best to last :-)
The Vertigo crew were commissioned by Microsoft to create an app in WPF that showed off some of the technology. What they came up with was a an app that helps build and visualise family trees.
Apparently genealogy is the fastest growing hobby in North America!
Anyway, they were interviewed at Mix as well so worth checking that out too.
Drum roll...
What they also did was release the source code (all 6.582 MB of it) so not only can you see how beautiful the application is on the outside, you can see how beautiful it is on the inside too!