Agreed, you can build great apps with html and js if you're prepared to spend the time, but it never quite feels like it's the right tool for the job. Flex has more in common with desktop widget toolkits and is a far better fit if your trying to develop anything with that sort of layout.

I'm always surprised these type of frameworks haven't caught on more. I built an admin system using Mozilla XUL a few years back. It's similar to flex in that it provides a cohesive framework with layouts and widgets geared to more traditional apps. It was a breeze to develop compared to the normal battle I have trying to get html and js to do what I want. Unfortunately Mozilla have only really got behind it as a way to develop FireFox plugins and seem to have missed the opportunity to promote it as general way to develop web apps.

I've always wondered how much flex is really tied to flash. Now flex has been thrown to the community I'd like to see someone try to modify it to use html canvas, svg or webgl as it's renderer (instead of flash). The low level rendering primitives would probably map quite closely. The bulk of flex is written in actionscript and mxml which could be compiled to javascript and then run directly in the browser.