Most of the desktop application development I do is in Swing, and I'm curious to hear people's thoughts on using JavaFX and/or Adobe Flex for building desktop applications. Have you had success building desktop apps with these? Or would you stick with Swing for now and use tools to help make Swing development more productive?
If you're making desktop apps, I'd stick to Swing. JavaFX/Flex/Silverlight would be more appropriate for RIA - rich internet apps. Although I'd argue that none of them would be a choice for the long term - looks to me like HTML5/CSS3/Ajax are winning the day, but thats a pretty subjective area. But for desktop apps - I'm a big fan of Swing (also Java Web Start is a very underrated technology)
I would say that JavaFX can be seen as a kind of extension of Swing with a new way of developing a Java GUI by using a declarative programming language: the JavaFX Script. JavaFX Script code looks exactly like a JSON script, unlike Adobe Flex or Microsoft Silverlight which uses an XML syntax.
JavaFX Script can interface with Java and therefore can call Swing components easily. It's really a new generation of GUI API, like Swing was for AWT: nice graphical components, new easy ways to manage layouts, really nice features to build dynamic interfaces: bindings, timers (to build animations), etc. Have a look here: http://www.javafx.com/samples/ and to the tutorials and see how fast you can build a kind of Google Picasa application... The API even contains some tools to use easily web services: you can find plenty of samples of GUI built in JavaFX connected to some public web services (like a Weather Forecast tool).
And the best... is the deployment part. You can embed your application within an html page, like an applet, and the user can drag and drop the application to her/his desktop to use it whenever she/he wants (without returning to its browser)!
Really, I think JavaFX, at its early stage though (v1.2), is a really good tool and represents the first step for Java toward the next generation of applications: the Rich Internet Applications (RIA).