Development of the next version of Flex, codenamed Gumbo, is well underway. I'd really encourage everyone to go [grab a build][1] and give it a whirl. I did because I wanted to see how I could take [a sample][2] I built with Flex 3, Degrafa, and AnimateColor and build the same thing with Flex Gumbo. Here's that version:
<iframe src="/SkinTransitions/SkinTransitions.html" width="400" height="100" frameborder="0"></iframe>

And here is the new version built with Gumbo and FXG (requires Flash Player 10):
<iframe src="/PrettyButton/PrettyButton.html" width="400" height="100" frameborder="0"></iframe>  

The code for this new version is pretty elegant. The interesting part is the custom skin:
<iframe src="/PrettyButton/srcview/source/PrettyButtonSkin.mxml.html" width="99%" height="750" style="border:1px #cccccc solid;"></iframe>

I had to write the FXG by hand which really wasn't very hard but ideally in the future a designer can just give me the FXG code, exported from their design tools.

This was a fun experiment. Let me know what you think of Flex Gumbo code for this new version.

 [1]: http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4
 [2]: http://www.jamesward.com/blog/2008/04/15/flex-3-skin-transitions-with-degrafa-and-animatecolor/