I’ve just played with CS3 for the first time, and I’ve gotta say, “WOW!”
Things that used to take me hours now take minutes, thanks to the new Puppet tool. No more do I have to take a file into photoshop, cut it up, place each piece on its own layer, import to AE, move anchor points, then animate. A few puppet pins, and start animating, followed by a few final tweaks.
Haven’t played with shape layers yet, but in my opinion, the Puppet tool makes the switch worthwhile.