http://www.insideria.com/2008/01/actionscript-30-is-it-hard-or.html

Colin Moock’s latest article for O’Reilly examines the difficulty of learning and using ActionScript 3.0, compared with ActionScript 2.0 and ActionScript 1.0.Executive summary: I argue that ActionScript 3.0 itself is not harder to learn or use than previous versions, but that there are some important issues in the Flash authoring tool that make ActionScript 3.0 less approachable for small-scale programs and inexperienced programmers. Specifically:1) on()/onClipEvent()-style events are gone2) parent.gotoAndPlay() requires a cast3) deactivating display assets that are no longer in use takes more workThe first two issues should be relatively easy to fix. The third might not be fixable at all. One other, more minor issue: you can’t dynamically change a symbol’s class at runtime (as previously possible via Object.registerClass()).