This is something that bothered me since a few months, even on Mavericks, as at the moment I am on Yosemite. Every now and again whenever theres something going on in the background (most of the time there is when it happens), the mouse seems to "spaz out" what I'm gathering it basically stops the mouse and then teleports it to where it was supposed to go, but much farther then it should go, at least thats the effect that I recognise. This started happening after having added a magic mouse to the mac, and then removing it to go back to my Razer Abyssus mouse, which always worked fine for the last four or so years I've had it. Also, to note this issue happens with all kinds of other USB mice, or on any surface. So mousepad/mouse issues are to be excluded. As of right now, I am testing the use of the mouse with it plugged into the usb port directly and not trough a usb hub, as at the moment in terms of hardware issues, thats the only other thing I can think of. In terms of OS issues, I've tried many things that were suggested to me, like "SmoothMouse" and other mice apps. So I ask, did anyone have such an issue in the past, and knows if its a system issue, that possibly can be solved? If so, would you be kind enough to instruct me on the matter? Its quite distracting to have this "spazzing" happen every now and again, so I'd love to find a fix for it.