If you haven’t viewed this video yet, then be prepared for some exciting stuff! This video demonstrates the way that tweens are created in Flash CS4 (code name, Diesel). Basically, keyframes have been taken out of the picture for a much more robust, organic way of creating tweens.
Also, it appears that the need for motion guide layers will vanish! Less layers means less clutter in the workspace! Can’t argue with that!
Anyways, I’ll shut up now. Here’s the video:



