Xbox is a bit comical
When it comes to doing anything other than playing games and before you lot start, yes I have PS3 & XBOX.
XBOX plays less video formats, requires you to be signed in (or did last time I tried) to play a film from a USB stick, never plays well with non-MS media server and, extra super comically, requires you to pay for a Gold memberhsip (£40/yr last time I looked) to stream vids from the Netflix/Lovefilm accounts You already pay for. What a monumental cock up THAT is.
PS3 in the other hand plays most formats (not MKV sadly), plays well with non-MS media servers (e.g. Mediatomb, uShare) and has free access to your own Netflix/Lovefilm accounts. Cinavia is a pain in the arse though. Oh and it plays BluRay.