It's a cool idea. I don't know how practical it is though. Like you said, it eliminates the need for expensive 3rd party equipment for recording gameplay, which is awesome.
In the Halo series, it's a cool novelty to pick out your coolest kills and send them to friends. I think I only messed with it in Halo 3, and never since. Uncharted 2 had that broadcast trophies to your twitter feed thing, which it sounds sorta like one of the social features that will be implemented into the OS its self. I don't know if that's what I want from a system, but that's probably just me being an old man.
The biggest game changer for me is being able to play something as soon as you start downloading.