I leave my caps on because they are yellow and they match my bike. Vanity.

I've never found any reason to believe they caused flats.............. whenever I have a flat, it's for a defined reason. The only time I've had problems with valves has been using a BAD excuse for a frame pump. Or a bad batch of tubes from the LBS, and they exchanged them gladly. I've actually never heard of valve caps causing flats........ maybe it's an urban myth.

annie