You can only fold AA if, by folding, you are GUARENTEED more money. So, in Pel's example - your $EV goes way, way up because 3 people are probably out of the tourney, so you get 2nd place for free.

So, I guess this would hold for a standard 9/10 player SNG when you hold AA in the BB and everyone goes all-in infront of you. You have a 99% chance of 2nd place if you fold, which is worth 60% of the the first place prize (which you have maybe a 30-40% chance of winning if you call)

Actually I am just restating what Pelion said. Post whore!