As I hinted in my other post, the CO2 is pretty much a necessity if you're under a time constraint, as in commuting to work - and it's definitely a matter of politeness if you're riding with others. If I did most of my riding alone I wouldn't bother with it. A "real" pump doesn't weigh any more than CO2 plus backup pump, and that's all I carry on the commuter. It's only on the roadie that I'm usually on a club ride and have to take other riders into consideration (and waning light, on an evening ride).