I use generic ink cartridges too - and with my previous printer, which was a Pixma, the printhead died and maybe that was due to using the non-Canon ink? I can't say for sure one way or another what actually happened to it, but I suspect that even if the generic stuff kills a printer off after a few years you would probably have saved enough to buy a new one anyway. I have a Canon TR8500 now and it's much quicker than the Pixma was at printing; the ink cartridges cost more than the ones for the Pixma, but they seem to last forever. (I've been buying them from E-Z Ink on Amazon.)
