I'm running on win7 and i have the same problem. Is just frustrating trying to hit 2 consecutive targets at the shooting range on the carrier, it seems almost impossible. I had the same problem in Arma 1 so i think its has something to do with the engine/mouse accel/mouse inertia/whatever. I've never had this issue in any other game (apart from arma1), even Bioshock works pretty well with my g9 (900 DPI, every other mouse related setting is default in the OS).
BTW, i also notice a little lag in placebo's vid. I'd like to see some other video from the people that say they don't have this problem (it would be a lot better if they could record it in the shooting range at the carrier or at the bootcamp).
My rig: 8800 gts 320 mb e6600 @ 3.0 ghz
In game settings: 1280x1024 everything normal settings except blur (low), 1600 view distance. Don't seem to have any low framerate just the occasional hiccup when turning too fast.
cheers.
Tomorrow i'll be trying some of the proposed fixes, and will post my results.