I have had 2 optical mice die on me in as many days. One was wired and the other used a wireless dongle.
I have unplugged and repluged them into USB ports quite alot between 2 computers recently. I rarely use the Safely Remove USB devices in the sytem tray as I thought this was more to do with protecting Windows rather than the USB devices themselves.
Is it likely that this has caused them to stop working?