With Flex, developers can create Flash-based apps with features such as chat, real-time dashboards, reliable messaging, and data push services designed to run in the revamped Flash Player 9 virtual machine. Flex 2 now supports server less, stand-alone app deployment as well - good for offline apps in need of periodic connectivity.
On the downside, companies with an investment in earlier versions of Flex face a bit of a migration hurdle. Although Version 1.5 apps will continue to run in Flash Player 9, they will need to be recompiled under Flex 2 to take advantage of any new capabilities, so prepare for some code parsing.
And, although the new Flash Player shows performance tweaks, debugging, and improved XML support, it is currently available only for Windows PCs and non-Intel based Macs - making this somewhat less flexible in customer-centric deployments.
Notably, Adobe is also working on an AJAX bridge and has done a 180 on its licensing structure - making Flex available free of charge and opening its source code to developers.
Specifically, the framework, SDK, and a basic version of the server-side data engine, Data Services Express, are free.
In all, I found Adobe Flex 2 a superb choice for streamlining development of enterprise-grade, data-driven RIA applications. With good built-in capability for real-time messaging, collaboration, and graphical data binding, Flex's muscle will help businesses break free of the constraints confining today's Web-based application delivery.