I have am currently on Window 7 RC at the moment and I have the same problem. The mouse just stops in its tracks and I hear a do do sound then it comes back. It might do it 3 times in a row or it might not come back after a couple hours but it is irritating when playing games. I was using a Razer Deathadder mouse when it started then I switched to a Logitech MX510 both opticals. The MX510 didnt do it for a while then it came back. Ive tried drivers for both. Ive tried in all usb ports still does it. It doesnt do this on my other computer so if anyone knows any fixes without reinstalling windows it would help. Thanks