Nice find, glad they have finally released this. There is a video demo from the TED conference here:
TED | Talks | Roy Gould, Curtis Wong: WorldWide Telescope (video)
Google earth also has a similar but less impressive feature:
Google Earth has a Sky function. Select "Switch to Sky" in the View pull down menu and Earth will disappear and become a celestial globe.
Yep went to have fun with this yesterday but there is a bug where it isn't always picking up the proxy settings from IE so I can only use offline mode, so no pretty pictures :(
Carried off with Microsoft's usual panache I see
MS whips lens cap off WorldWide Telescope | The Register