After a quick Ctrl-F through for Flex, I see only three references - I think that the signal to noise ratio (noise presumably being PHP, ASP and any % % stuff [Python Server Pages etc] is low enough for me to have to give Flex a fourth nod. The reason Flex (and similar things like Silverlight) can get around the tag madness is that they don’t do HTML, so they define UIs declaratively in a manner much more akin to normal (desktop) application development. Since the page production doesn’t consist of a top-to-bottom evaluation (basically a big Main function) you can write proper event-driven code and perform all the user interaction on the client, where it belongs, without having to deal with Javascript browser incompatibilities.
Without wanting to sound too much like a Flex fanboy, I have to say that it’s a lot easier to write good code in Flex / Actionscript than it is in ASP/C#, HTML/PHP, or any other server-side framework. Write web services / REST services to deal with the server-side stuff and design a nice event-driven UI for the client. You shouldn’t be worrying about transmitting forms over the wire in HTML. Try it, you might like it 
