I am running System Version 10.8.5 on a 21 inch IMac and lately my mouse seems to be unsmooth and erratic, sometimes jumping to other parts of the screen. It is a wireless mouse that came with the computer when I bought it (3)? years ago. Very annoying. From what I can see in a quick search I am not the only person suffering from this. Wish I could fix it since a lot of what I do requires some degree of smoothness from my mouse.