I don't know if anyone has pinpointed a specific cause, but some people have said switching vsync on/off has removed the lag. You could also try a different USB port or reduce the polling rate on the mouse. What are your system specs?
From personal experience, my old laptop could not handle 1000Hz or 500Hz polling rate, 333Hz was the highest without issues. The mouse and laptop: Logitech G500, w/HP Pavilion DV6. i5 430m, GT 210m, 4Gb RAM. The CPU would always be at 25 - 30% load with a high polling rate. Only happened playing Borderlands and Skyrim, Vsync off in Nvidia Control Panel.