Animating in CS4 running very slow compared to CS3?

On Flash Kit there is a thread that is worrying me because I haven’t used CS4 yet but by the sounds of things people are finding it run really slow when you use CS4 for animating or open a CS3 file that would normally run fast.

So far we’ve only heard from Mac users, has anyone on PC found the same thing?

http://board.flashkit.com/board/showthread.php?t=780172