Why not Flex?
cookiecaper: I have a client using Flex right now. They're having a desperately hard time finding anyone adequately qualified to perform the work, so availability of hackers is an important consideration.Also, everything else people have said. It uses a plugin, which slows things down and appears non-native. It's proprietary; if one day Adobe says "Flash Player is universal, let's start charging for it, and jack the IDE cost up 50%. We don't care if everyone moves off of it because we'll make a lot more money off of the relatively short-lived mass influx of license money", or "Let's just not release the new version or ensure compatibility on (Windows 7/OS X 10.6/Linux/Solaris/any other platform important to your userbase) [yet]", or "Let's break compatibility in Flash Player 11 and make a really difficult downgrade path", you and your users are kind of screwed, and so on.