I've been developing some materials in JavaFX recently.
The performance of JavaFX has improved markedly over the last 6 months (between 1.0 and 1.2), and is supposed to improve yet again with the 1.3 release.
"Out of browser integration" is essentially JNLP (ie, Web-start). It's perfectly reasonable from what I can tell. For instance, WidgetFX have written a Vista/7-like desktop sidebar entirely in JavaFX http://widgetfx.org/
There is supposedly "momentum and drive" from Oracle -- Larry Ellison has been publicly enthusing about it -- but that of course is held up by the EU's investigation of the Oracle-Sun merger.
Note that JavaFX does not use Java syntax. It is, however, a very concise and quick language to write a GUI in, but does have a (relatively short) learning curve of its own. It can however include any Swing components (and there are quite a few libraries of them out there), and can use Java classes.