If you're unconvinced that Windows Presentation Foundation is more than just a glitzy UI, you should take a look at Microsoft Codename Max. We announced this during Jim Allchin's PDC keynote, and it's a fantastic photo sharing application built entirely using Windows Presentation Foundation that demonstrates the how 2D and 3D, data binding and animation can be used together to build an application that would be hard to write any other way.

You can download Max from their website - it uses a neat streaming update mechanism to keep your machine up to date. Make sure you have the PDC build of WinFX Runtime Components on your machine prior to running it for the first time.

Have fun!