For what it's worth, I noticed I was having fps drops worse than when I used to run the card on my old 8800 GT.

I tweaked the settings by turning AA completely off, turned AS x16 and turned everything else to max. Problem appears to be solved without the need for a reboot, as I went directly from choppy fps to clean fps that you'd expect from this game on a decent system.

Hope this helps!
~Cym

I can confirm this, after a few days I got the stuttering movement, too, and restarting my computer got rid of it. Strange bug.

I get this problem now as well. Restarting helps, but it's still pretty jittery, its somewhat playable but it's annoying as hell. It seems to hate AMD quad-core's for some reason. My Laptop is more than powerful enough for a game this old too :/