Other: The controller.
Since the PS1, I have been primarily a Playstation Gamer (tho I absolutely love my DC). Keeping the same controller (for the most part) was my primary reason for sticking with the PS3. Dont get me wrong here, there is NOTHING wrong with the 360 controller, it just never felt right to me.
Bought 2 of each of those consoles on day 1 (sold 1 of each on ebay for metricfucktons of money) and just ended up sticking with my PS3 (gave my 360 to my g/f about 2 years ago after a RRoD warranty repair).