Dont buy the PS3 based on GT5.
You'll soon be bored of it after a couple of months, when you get to a point where you are racing for 30 laps in the front all on your own for ages on end just as in GT 1, 2, 3 and 4!
Pessimism aside it will be a supurb game but wont be the be all and end all of gaming.
PS3 = much better build, cheap BD player (you WILL need an HD telly for that!). However, they have had failures, esp with the new 40 GB units, but not as much as xbox
360 = better games at present, and more importantly, much better on line gaming and that part wont change.