Update,
I had played the demo on my work machine (P4 3.4G, 3Gig, 256M 6800GT), and I noticed A LOT of mouse lag, much like PA (I think it was PA, at least until they released a patch for it).
But then, I go and play it on my home rig (2.4 6600 C2D OC'd to 3.2, 2G, 8800GTX SLi), and had NO mouse lag whatsoever. Like schneiderguy, it push both Cores to 100% w/all settings maxxed. The whole experience was MUCH more enjoyable than the first time........
The 'lean right or left' thing is kinda weird to me. I dont know if I have to adjust my aim or not....lol!