One of the most interesting things is the white space on my desktop. The F3 Calculator is part of it actually (or vice versa really.) There's probably some bugs to be worked on here! Also notice the little F3 icon in my system tray. You have to use that to close the calculator. The whole thing launches using Java Web Start, which is a good thing.
So yeah, JavaFX has a lot in common with Flex and SilverLight. Even in name. Microsoft had WinFX which became Windows Presentation Foundation which became Windows Presentation Foundation / Everywhere which became SilverLight. I'll say some of the same things about JavaFX as I said about SilverLight. If they could actually achieve "my dream" of writing a UI once and having it render nicely as a web app, a desktop app, and (most importantly) a mobile app, then it will be a huge success. I don't think anyone is close to that, yet.
JavaFX could actually have a lot more legs to it than SilverLight. It will be completely open, unlike either of its competitors. That should give it a huge advantage. That open nature should also mean a lot of creative integrations with the huge open source Java ecosystem. That's how JavaFX could win over developers. The key will be for Sun et. al. to deliver adequate tooling for it, as it is a UI language. Adobe already provides good tooling and Microsoft is sure to do the same. Sun's doesn't have to be as good as the Flex/SilverLight tooling, but it needs to be close. If it's not as good, you can expect to see other folks in the Java community step in.
Speaking of tooling, Cedric has a good rant against JavaFX. He smelled Sun trying to get people to use NetBeans, but as you'll see in the comments, there is an Eclipse plugin. Maybe the Jigloo guys can work with it, too. The better point that he makes is that Groovy SwingBuilder does a lot of the things that JavaFX promises to do. Maybe Sun should have leveraged that. I haven't tried JavaFX out yet, so I can't say if it has any syntactical advantages over Groovy. I must agree with another commenter that Sun doesn't seem too fond of Groovy. They seem much more interested in embracing Ruby via JRuby.
Update: I tried out the JavaFX plugin for Eclipse last night. It is quite bare-bones. It basically just lets you run a .fx file from Eclipse. No visual editing. It didn't even seem like there was any extra syntax help. I will try out the NetBeans one, but it sure looks like Cedric was right on about Sun once again trying to push NetBeans on people.