I'm working on this new project which will span a year. So it's apparent we may need to upgrade to AS3 at some point and require code migration from AS2 to AS3. Big Spaceship works closely with Adobe and we're running with Flash CS3, the next Flash Professional IDE.
Looks like I've put off learning AS3 long enough. AS3 blows AS2 out of the water. The debugging is so much more stricter, the API is cleaner, the code is more powerful, and the possibilities are endless. There's more on every front.
Guess I should probably throw in the usual shameless plug, go sign up for a preorder of Flash CS3.