Heres some thoughts of mine.
Rock solid. No stability issues.
Mouse and keyboard support (atleast in UT3)
Ability to run another OS
Mods for games like ut3
Blu-Ray (extra storage, no disc swapping)
Controller may be used with PC (also true of 360)
Better games (for now)
Xbox live - more features than PS online
Controller may be used with PC (also true of PS3)
DVD (less storage, disc swapping soon to be)
Xbox live monthly fee
less freedom on what one can do with the hardware
Unreliable at times (overheats, red ring of death, slow repair times, etc)
Honestly, I wouldn't get either right now.
The PS3 games suck, and the 360 over heats and dies like none other.
Overall, in the long run, the PS3 WILL be better. It's ability to use mods in UT3 really, and I mean REALLY changed my outlook of it.
MS demands money for anything that is mod related, sony doesn't care.
I hate sony AND microsoft, but now I hate sony just a little less.
PC Gaming FTW