I wonder how the apps are going to play out. XNA is used for the games and there are plenty of shops out there creating for xbox. It looks like porting existing XNA games to the phone will be fairly straightforward. I'm expecting Windows Phone 7 to be a big player in handheld gaming because of XNA/Xbox.

I'm primarily a .Net/Silverlight dev myself so I'm biased but the core development experience is better than Apple/Google IMHO. They do need to get off their asses and release more controls (like the pivot) or they aren't going to have standardized UI across apps.