I get this exact problem! I have a Razer Copperhead mouse and never had this problem before until I installed Win 7 Ultimate x64. I do, however, notice that the problem is less frequent (dropping the mouse down that is) when I stop some processes, and an NVidia customer experience process seems to make the most difference. But I cannot get the problem to go away completely! I am sure it is a service or process that is causing the problem as it doesn't happen in safe mode oddly enough.
Any help would be greatly appreciated
And if I get the problem completely solved I will post how I did it.