I was wondering how the Steam box would/could affect Xbox this time around. 360 has quite a few titles that aren't on PS3 but are on PC, so were essentially exclusive on your TV.
The appeal of the 360 is really enormously diminished if you compare it to a gaming PC, though. Take a look at the Top 10 360 games lists (either of all time or year-by-year since its launch) and most of them are on PC and better on PC. PC has the 360 controller and a ridiculous choice of other controllers, free online, etc.