If a paint can is only part used, inflate a baloon, and put it in the can with the paint, to help keep it from drying out. OR, for those who have a propane torch handy, run the torch unlit into the paint can for a few seconds. This displaces the oxygen, and prevents the paint from drying out. I havent tried this myself, but have a few friends that swear this works.
The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done."