In a recent podcast put out by the good guys over at JavaPosse, Brian Goetz made an interesting comment near the end
JavaFX code compiles down to ordinary Java classes, so a simple JavaFX program can run anywhere you have a JVM. now hardware support for acceleration is different for different devices, but the intention is to have a program that will run on a phone, on a desktop, on an Applet, in a Blueray device, anywhere where Java can run. Flash dominates in the RIA space and there is excellent support in Windows, and pretty good support on the mac, and random support on other platforms. Java has the advantage where there is good JVM support on many more platforms, including mobile platforms. ~ Brian Goetz
If having your application work mobile and on the desktop and in the browser matters to you, I feel this will be a big consideration for you when choosing your RIA platform