What a great sample application to showcase the power of Silverlight.  Popfly is a mash-up creation tool that's super easy to use and fairly powerful for an alpha.  This video gives a 15 minute overview of the Popfly functionality, featuring integration with Windows Live Spaces, the World of Warcraft guild data, and Microsoft Virtual Earth.  Very cool stuff!!!  I like how it allows us to share our mashups with other users in multiple ways, and that you can customize those that you share down from others...  I can't wait to see more from this team!