Flex 3.0 and AIR 1.0 are here. Congrats to the teams, and I hope they're all getting some sleep now. Even more interesting to me is the open sourcing of the Flex compiler and framework. It's something which may get lost in the shuffle today, especially without a lot of developer documentation out there yet, but there's a lot to dive into.
Once you get the source, you'll have Eclipse project files in the 'development' folder. You can compile easily and start seeing what you can break. I was just poking around, and I'm remembering a number of interesting files to look at:
flex2.tools.Compiler, the entry-point for mxmlc
flex2.tools.Compc, the entry-point for compc
flex2.tools.flexbuilder.*, the interface to FlexBuilder
flex2.compiler.as3.EmbedEvaluator and flex2.compiler.*Transcoder, the heart of Embed
*.vm files like flex2/compiler/binding/BindableProperty.vm for some interesting codegen
flex2.linker.FlexMovie, the confusing guts of the Flex SWF
I see something I'm going to look at already, a simple change I'll try to blog about this week.