Yo, I just stumbled on this (rather oddly worded) PDF and accompanying (rather pointless) example code regarding squeezing some extra speed out of your ActionScript:
Tips for tuning ActionScript 3.0 performance for Flex and Flash developers
It’s a good read. For instance, did you know that accessing elements in an Array is quicker if the one you’re accessing is in a denser area of the Array? I sure didn’t! And now I do. So read up.