In D2:ED, one person found that having a specific program running in the background (used to allow control of multiple networked computers with the same keyboard and mouse) caused the mouse to be extremely sensitive controlling the camera, etc.
A few people had lag issue with the mouse pointer, as well (part of the reason the original release of DKS was set to limit the FPS to 30, though that can be changed in the options in the patched game).
