I had a frame pump fail once in 25 years. So I carry a CO2 cartridge, but have never needed to use it. I feel better having it, and if I am ever riding with a group or "for a time" I will use the CO2, and hope the cartridge is still good.

I'm in the same camp as 79pmooney. Every bike gets a frame pump as well as its own saddlebag with multitool, patch kit, and levers. I don't move pumps from bike to bike between rides.