I used to be a huge GT fan. I still dig out GT4 every so often and do a couple laps around the 'ring. Admittedly, since Forza 2, I haven't touched it.
It's going to take a lot to convince me to buy a PS3. Will GT5 be enough? I don't know. GT3 got me to buy a PS2, but it was $300 cheaper than the PS3 is.
We have PS3s here at work, and they never get touched. Maybe it's cyclic, and we tend to look at 360 games more because our direct competition is on that console. I don't know. I just think, in an office literally staffed with game nerds, it's very telling that shiny new game consoles are totally neglected. I won't go into specifics, but suffice it to say that the launches of the 360 and PS3, and their effects on the staff here, were markedly different.
I might be swayed to buy GT5 and play it here at work, but I can't imagine actually buying my own PS3 for it. That's sad for me to say, because I really did love the PS2...even though it was
such a pain in the ass to develop for.