bought an intellimouse optical for my dad's machine, then I got a letter from MS saying there were probs with it and send them proof of purchase and they'd send a new one. I did. They did. They both work fine! Then i bought a Labtec Optical for machine #3. I know that I like the optical so I don't have to clean out the crap off of the little rails like I did before, other than that I don't notice much difference between mice in general and the MS and the Labtec in particular.