Oh boy, time really flies. Was it really 5 years ago when I was struggling to move from the very comfortable AS2 to a shiny new language where the "usual hacks" were not working anymore?!
I must admit that at the beginning I had a hard time adapting. The movieclip properties suddenly lost the preceding dash, so movie._x was not working anymore. Then came the percentage values that changed from [0..100] range to [0..1], like alpha and volume, and adding event listeners for mouse actions. Last but not least, the best part, a much bigger Flash Player API, with lots of new cool stuff to try out.
Today, looking back at Actionscript 2, I realize how complex, robust and mature Actionscript 3 has actually become. It's a true programming language and I'm glad that I get to use it every day.

Here's a nice migration list with the main changes between AS2 and 3 : http://livedocs.adobe.com/flash/9.0/ActionScriptLangRefV3/migration.html

Happy birthday Actionscript 3!