http://jsfiddle.net/MrkY9/
My computer (and so far, no other computer among my coworkers) is exhibiting an issue in Chrome, IE, and Safari (but not in Firefox). Sim
Ok, I found the problem, though I don't fully understand why it was an issue.
I had Task Manager running in the background. And for some reason, every time it updated itself, it was causing IE, Safari and Chrome to receive a mousemove event.
It doesn't make sense, but at least the fix is simple: close the Task Manager.
(It's very obvious if you are in the Applications tab. If you're in Performance, it depends on what the values are set to.)