CO2 is great when you have it. What happens when you've discharged all the cartridges you have, and then you need to inflate another tube? Members of my club have had to rescue weight weenies who ride with only 1 spare tube and 1 CO2 cartridge and their attempt at fixing their flat failed.

Also, look up Leonard Zinn's online column about bike repair: butyl tubes are much more permeable to CO2 than plain old air. After a day or so, you'll have to reinflate the tube with air as the CO2 will have leaked through the butyl. (Don't if the same holds true for latex tubes.)