I just happen to be a Java developer writing Flash-remoting code. Our Flash clients (in the browser and in a Windows wrapper) ActionScript 2 code accesses my server side code via AMF and HTTP.
We are about to start a new UI development effort with Flex 2...so this is all very interesting to me. My initial research suggests that ActionScript 3, which comes with Flex 2, will allow closer data type binding. That is something I am excited about. The Flex 2 Builder also looks to dramatically increase our UI guy's productivity...along with lots of new and sexy UI components. The only catch is the client side Flash 9 player requirement. (Flash 7+ is almost universal.)
We begin full time research and prototyping next week. I am excited.
"Flex is a short term deal." There are legions of Flash developers loyal to Adobe out there and are moving their way towards Flex. They are not going to disappear or retrain in Java. The first version of Flex was released over two years ago. Adobe, IMHO, has done a very good job of stewarding client side Flash as the way to provide rich multimedia client experiences over the web. There is no reason to think they'd muck it up anytime soon allowing a competing, open approach (read Java) to replace it.
(This all ties in with the "why is Flash more popular than Java in the browser" debate. My read is that a) Flash is more prevalent than Java on the client side, b) it is relatively easy-peasy for a UI developer to whip up something pretty for Flash players, and c) "web designers" (and other non hard core programmers) have been making many presentation technology decisions for *years*...and choosing Flash.)
"Flex is proprietary and has only one vendor." Proprietary, yes. But there are more vendors coming out. Check out http://www.osflash.org/ . Of them my company is specifically interested in Red5, an open source Flash server. The project is one year and the future looks bright.
So, Steve, I think Flex has a future and increasing numbers of us server-side java coders will be writing services for client side Flash.