Quick feature list here, or Adobe’s take on things here.
I’m hoping the release smoothes the transition from ActionScript 2.0 to ActionScript 3.0 for designers, as I’ve a few workflow fears for what the new language may mean for production houses (especially if also using Flex 2.01). I don’t think Adobe’s claim that AS3 will enable production houses to “save time” will immediately ring true, going by initial research into Flex and some gotchas when combining AS1/2 content with AS3 content.