In No-limit, I throw away Bullets fairly often especially when I play them aggressively and I end up getting re-raised, you can usually tell when they are no good.

In Limit, I'll usually "Elephant" my way down to the river if there is only one other opponent and he is re-raising my re-raises, especially since I play AA as aggressive as possible. I will toss them with multiple opponents when the betting is capped on the flop, I'll always bet and or re-raise the flop with AA. Again you can usually tell when your aces are dead. So basically if someone beats my AA heads-up I'll pay them, but I won't pay with multiple opponents betting their asses off.