JavaFX has been announced twice, at subsequent JavaOnes, in 2007 and 2008. It started out as F3 (which stood for Form Follows Function), created by Chris Oliver as a Flash competitor for Java. Its main emphasis, as a scripting language, has been to make it easier to do graphics and web 2.0 interfaces with Java. In many ways, it has achieved this goal, twice.
F3 - http://en.wikipedia.org/wiki/F3_(language)
But from what I hear, it's going to be taking a different direction. First of all, what started out as an open-source project will more than likely go closed source. Second, the rumor is that it will focus more on 3D graphics and animations, taking advantage of graphics acceleration and OpenGL built into today's desktop computers, and many mobile devices such as the iPhone, and the future Android-based platforms.
This is a key evolution of what may become the quintessential Java graphics platform for two reasons. First, being closed-source more than likely won't affect developer adoption (so long as developers can still build applications on top without issue); second, it provides Sun the "secret sauce" it needs to make its open-source Java FX Mobile platform more appealing, and hence to gather more licensees.
Having the proprietary bits, and added value, to put on top of an open-source technology allows you to maintain a competitive advantage in an otherwise socialistic software economy. However, the ability to do such a thing may be encumbered by the GPL itself. In other words, the viral effect may very well infect the "secret sauce," close-source Java FX graphics libraries that Sun is rumored to be building. It will be interesting to see how this unfolds.