I've tried it. Hooked up to Virtual GT simulator and 1080P TV (and 5 other machines). It was very good.
Small niggles. Real time on-car shadow rendering had some issues. I don't know what was up with the anti-collision thing. (It made sense, but it only worked selectively, not the entire time, so I didn't like it.) The short cut penalty was annoying too. (Again, it made sense for online based gaming, but it worked some of the times and not all the time.) Oh, and I still can't over that tire noise. And Finally, I was stuck with the Lexus IS-F on Fuji, I couldn't try anything else. (But that was Lexus's fault, not Polyphony's
)
Well, the prologue is still technically a demo, so I hope the real thing's (even) better. And it'll probably be the best looking racing game for a while. So +1 for Polyphony.