I like the idea of the Tile-based UI for a mobile device, where the device's purpose is various quick-scan information-based apps.
I'm not sure I see where a Tile-based UI for a desktop environment makes any sense. My day-to-day computer usage is roughly divided between the following applications:
Textmate
XCode
Photoshop
Aperture
Email
MS Office
OmniGraffle
Web Browser (where I regularly browse between roughly a dozen different sites, plus occasional surfing).
Other than email, how are "Tiles" going to help me with any of those applications? What kind of "live information" would an "Aperture" or "Photoshop" tile usefully be able to tell me?
Granted, most of these are Mac applications, but substitute the above applications for Windows-centric apps, and I still fail to see how my work day is in any way improved by a "Live Tiles" UI.