I was an avid user of JavaFX 1 (1.0 to 1.3), but I haven't tried JavaFX 2 yet, partly because it is beta, partly because the long wait douched my enthusiasm, partly because there is now lot of stuff to re-learn and mostly because I just lack time...
That, and as pointed out, increased support for Canvas and JavaScript libraries across browser (and better JS performance) made this a lot less appealing. Windows only support (currently) is also a weak point. So is the size of applications (at least until it is integrated to the JVM).
Now, I can see where it can shine (with regard to JS only): speed, and perhaps memory usage. I see nice JavaScript Box2D demos, for example, but even on my modern home computer (as opposed to my old work computer...), I can see significant lags, probably at garbage collection time.
I am still hesitant to invest time there... from a personal point of view; enterprise usage is a very different matter. The strong commitment for a big enterprise (Oracle) add weight to this technology. Well, if I should do JavaFX for work, I would be happy to dive again. ^_^ Even better if it is with Scala! :-D