I bought this and hooked up my G25 to it.
1080i doesn't do this game justice. It was designed for 1080p, anything lower and you get AA artifacts and rough edges. That said, you don't notice it too much when you're actually driving.
Physics wise, while it doesn't hold up to the likes of LFS or rFactor with RealFeel, it's a giant leap from previous GT releases. I don't get quite the same level of detailed Force Feedback that I do in LFS, but it's decent and doesn't immediately seem like canned effects.
As for the actual racing, I'm enjoying it way more than Forza 2... the races have well-matched groups of cars, and you can't just slap on some power-enhancing part, magically remain in the same class and dominate a race. I really enjoy that you can't just get around being a lousy driver with mods
That said, the AI is bland, predictable and timid. I've yet to jump online since I'm still mastering the tracks, but I'm sure it'll be much more interesting!
As for PC release, there's no reason a PC couldn't run this game. The PS3 isn't necessarily very powerful... the developers simply utilize those nifty vector processing Cell processors packed into the PS3. With NVidia's 8000-series cards attaining PhysX processing onboard, I'm pretty sure any decent gaming rig out in 2009 (when we can expect a PC release) will probably do a better job graphics AND physics-wise than current gen consoles.