So basically, the open source community made a better flash than Adobe did? That is rather amazing considering the resources of the respective groups.
Then when AS3 came out they seem to have thought "Oh come on!" given the quality of the compiler and language features so they built a better language. Again, faster and better compilation, as well as properly implemented things like generics (particularly compared to the awful implementation in AS3).
It's a lovely little language, and cross compiles to a vast range of platforms with ease. I built an android app which ran a webserver to control a TV app built in it (compiled to JS). I also had good success compiling it to PHP (cross-platform serialisation & deserialisation turned out to be easier and more performant than parsing XML on some low power devices).
MotionTwin made my working day so much better, not having to use the CS4 was wonderful.
[1] http://labs.adobe.com/technologies/alchemy/ [2] http://blogs.adobe.com/flashplayer/2011/09/updates-from-the-... [3] http://ncannasse.fr/blog/virtual_memory_api [4] http://www.adobe.com/devnet/pixelbender.html [5] http://ncannasse.fr/blog/announcing_hxsl