I've got a fairly new PC but when moving the mouse across the screen, the pointer jerks as if the PC is freezing momentarily every second or so. Strangely, this only seems to happen if the signal from the wifi router is bad. If I move the PC closer to the router to get a full signal, it's fine.
It also seems to affect the keyboard; Opening notepad and holding down a key shows the same momentary freezes.
-- Update: It's a logitech wireless mouse, and a wired USB logitech keyboard.