I recently used FlashBuilder 4.5 to package one of the AS3 games I designed for the Android Market.
When I started on the game, it was immediately following Apple’s announcement that it would be possible to create iOS apps using Flash, so I made sure to use pure AS3, and no Flex components. The result is a pretty decent framerate. I obviously had to make a bunch of changes to the game in order to accommodate the touch-screen, but for the most part it was pretty straight-forward. Adobe even included the ability to debug the app on the device, which is awesome. (Going to iOS is a bit harder but we should be able to do it shortly.)
Fortunately, I am lucky enough to work at NBC Universal, so I had the luxury of having help from Adobe! Thanks Jens!