I think it was on poker after dark that the host ( I forget her name) asked Phil Helmuth if there was ever a situation in which he would fold AA preflop and his response was a resounding "No"
Folding AA preflop is just crazy, even if your facing an all in raise because your going to be a 4 to 1 favorite heads up: how else are you going to get preflop odds
Now post flop, there definitely are occassions where you can fold AA... If you have AsAd, and the flop comes 3c4c5c, then you may want to fold, depending how many people are in the hand and what sort of raise your facing, because if any club comes on the turn or the river your gonna lose the hand, and someone may already have caught a flush.
The biggest problem with a hand like AK or AA is that people get very attached to hands like that and get to a point where they simply are unable to lay the hand down no matter the flop comes, or how strong their opponents seem to be playing the hand...
So fold AA preflop, No, Post flop Maybe, but one thing thats important is that you raise preflop so that you knock out the 2c7c for if the flop comes 3c4c5c.