Pretty cool... Faisal Khan recreated the iPhone UI with Silverlight and shows how you can do it, too.

http://dotnetslackers.com/articles/silverlight/IPhone-UI-with-Silverlight-2-beta-2.aspx

This will be really cool once Silverlight for mobile starts to become pervasive.  I can picture someone creating a new shell UI with Silverlight that looks like this.