These "mouse" sensors not only allow motion detection of small mice, motion detection of larger object and faster movement are possible too, which I think is a interesting application:
Speaking of interesting applications, the Roomba 980 uses an optical tracking sensor in order to improve the accuracy of its mapping -- inconsistently gripping wheels make it impossible to navigate accurately on earlier models (hence the "bounce around randomly" approach) but watching the floor move past gives far more accurate positioning data than simply counting wheel rotations.
They're really neat and there are tons of applications, but I've never been able to find good, usable packages to use with my own projects. Once in a blue moon one of the usual suspects will release a custom board. I just wish I could easily order assemblies from digikey, et al.
yes thats what I meant, I checked ebay and it seems I have outdated information, there _was_ a kit based on mouse sensor, but its no longer available. There are camera kits now providing same function, probably thanks to jump in cheap processing power (16mhz avr VS 180mhz arm f4).