synergy. microsoft will succeed if they can leverage the popularity of xbox live and put games/social media apps into devices that sync with xbox. i think they're nudging developers in that direction with the new xna framework. i've only briefly looked at it, but xna seems like a solid foundation for any type of rich media app.
as a consumer, i think it would be great if they converged zune and windows mobile all together. just throw a phone on top of a zune and you'd have a killer device.
//dreaming of course