I cleaned the bottom of the mouse because I think that was the problem based on the way you explained it. It does seem better. Maybe it's just in my head though.
I just tried Metro 2033 and another weird thing was happening with the mouse. This is much more serious though. IDK what it is, but it's really bad. It doesn't happen all the time. You can see the the frames kind of freeze/skip or something.http://www.youtube.com/watch?v=n9hVn08HrKw
I'm playing at max settings in 720p and don't go below 30 fps. I usually am around 40 to 60.