Love it! Get it!
Update: I guess words were in order (doh!). The fine print:
This application brings together the many compelling platform capabilities of Silverlight 4 into a rich out-of-browser application in the familiar context of Facebook.Enjoy the photos, feeds, events, friends’ walls, and inbox mail from your Facebook account in an appealing and user-friendly environment.
Note: Silverlight Client for Facebook is a Silverlight 4 developer preview application. When Silverlight 4 is finally released you may be required to uninstall and re-install the plugin. In order to install Silverlight Client for Facebook, you will need to install the Silverlight 4 beta first. After installing, return to this page.
I updated the links to get the application from http://www.silverlight.net/content/samples/apps/facebookclient/.