A few things to add:
Xbox has a clear controller advantage
Xbox has built a UI that is proven and that an entire generation of gamers have been playing on - links to friends, online content, tv, internet, etc
Buying patterns in the next cycle will be as much about social aspects as they will be about graphical prowess and exclusive content:
Massive head start and edge on social for Xbox
Graphical edge to Sony although it remains to be seen how big of a difference...