Learning Flex

I'm learning Adobe Flex now. Surprisingly, I have much better impression than I expected about it (my expectations are derived from one or two evening experience with Flash).
I dislike ajax/comet etc, because IMHO web browsers are not suitable for desktop-like UI and it is high time for a new cross-platform client technology.
Flex Builder resembles old good Borland Delphi or MS VisualStudio. Flex libraries and tools have "open design" (my intuitive definition for this: if there is no standard TreeView class, we could write it ourselves because all base classes/interactions are understandably defined and the sources are available).
BTW, interesting facts about the language. Adobe claims that ActionScript is based on ECMAScript Edition 4. The ECMAScript 4 language is in some sense progressive, has interesting (in particular lisp-like) features: http://www.ecmascript.org/es4/spec/overview.pdf. Also funny is that the reference implementation of ECMAScript is created on Standard ML.