Since yesterday, the Microsoft.com homepage has been promoting a new game for Xbox 360 called, "Scene It? Lights, Camera, Action" with a new twist- a mini-game embedded in the ad  itself.  I can recommend this game personally as it's been playtested by our family and friends at recent gatherings.   The game itself takes over the entire top panel of the MS.com homepage interactively in what I believe is a first.

Expect a lot more of these kinds of interactive experiences on the MS.com site and others to come in Silverlight. 

Microsoft Homepage