You can force garbage collection if you know you'll have some time where frame skipping doesn't matter (end of a level, menu, etc) with flash.system.pauseForGCIfCollectionImminent(). I've never had a problem with it though.
Good tips, especially copyPx
Jonesboro
Good Flash code is an oxymoron.
WarpZone
Did I say this would make your code good?
I'll be happy if you write ugly code that doesn't break the 500th time an enemy fires a shot.