Why not Flex?
nostrademons: It's user-hostile.Flex code runs inside a sandbox element, much like Java applets.  It doesn't feel native to the browser - the Flex app can change things only within its own little canvas.  (Okay, there's ExternalInterface as well, but then you're back to writing JavaScript and DOM manipulations.)  It's not aware of browser resizing - you're locked into a fixed width layout.  It can easily result in horizontal scrolling if you have a full-width Flex app in a small browser window.  It generally doesn't show up on mobile devices.  It takes forever to load.  It disables UI conventions - like being able to right-click on the page - that users are used to.  Hitting Ctrl-T when a Flash app has focus does not open a new tab.  It's not easily indexable by search engines.I look at it as Flex:Javascript::Swing:native GUIs.  It makes development easier, but at the cost of never quite meshing right with the rest of the platform.  You may like it, but your users probably won't.