If a dynamic language layer is the big surprise at Mix 07 it would be the worst kept secret ever. Wink MS hired John Lam for cryin' out loud. They've GOT to have something dealing with Ruby and the CLR coming out.

It'd be like hiring Eddie Van Halen to play oboe for your rock band.

I'll throw out my two guesses.

Universal Gadget platform.

Office apps online w/full web based APIs.