I carry Corbon ammo exclusively and I usually buy two boxes about every six months. So I guess I change mine about the same as everyone else so far. I don't really plan it out, but after it has been loaded for a while Ill just shoot it one day at the range.
Another thing I will do is unload the mag and change the position of the cartridges in the magazine every once in a while. That way the same round isn't being chambered and unchambered all of the time. Since I always carry one in the hole, I will rack the slide everytime I pick it up when Im going out the door. Then as soon as I get home Ill unload the gun, load the cartridge back in the mag, put the mag back in the gun, holster it and put it back in its cubby hole till I leave again.
I don't know if it really makes a difference, I doubt it does, but it makes me feel better not abusing the same cartridge over and over. Then they all get chewed up equally.
Michael