About the only time I will limp with AA is if I'm heads up or it's folded around to me in the SB. Occasionally, if I have a really reliable maniac to my left who I know is going to raise, I'll limp, then push (or at least make it too expensive for anyone else to call).
The thing you need to keep in mind is that AA is just another hand. PPL get too emotionally attached to them and would rather go broke than lose with them. The truth is that you will generally either win a small-to-medium size pot, or lose a monster pot with AA.
As with everything, the way to play aces depends on the table, the stacks, etc. Generally, make an average sized raise (usually 3-4 BB, but more if the table is particularly aggressive). However, if 3 or 4 (or more) people have limped in before me, I'll make a pot-sized raise (i.e. call, then raise the pot) to make it too expensive for most of them to call.
After the flop, be prepared to check it down or throw it away if it's a particularly ugly flop (e.g. 3 connectors or 3 suited cards, high pair, etc.). If not, another pot-sized bet is in order.
The idea is to play them aggressively, but don't go broke if you can help it. Like the lady says, "when you're beat, you're beat".