What happens to all the bullet fired into the air?

Just been watching the "good guys" in the opposition forces in Libya. You can spot the good guys as they have AK47s that they keep firing straight up in the air. What happens to all those bullets fired in the advancement of democracy? Do they just keep on going into space or maybe they turn into ice cream sundaes before returning to earth. I think there's an opening in the market for Kevlar umbrellas.