It has been quite some time since I used a Swing based Java application. Compared to beauty and close-to-native feeling of Eclipse based application, Swing just did not feel right - it looked differently and behaved a bit differently. For long time, my desktop was Swing-free (not counting the JDK demo). Not any more, though.
What made me to reconsider, is new release of the Netbeans v 6. In the latest milestone builds (M6 to M9), Netbeans team built amazing Ruby development environment. Compared to Ruby plugin in Eclipse, it has way more functionality, better debugging, really impressive editing support and very cool Rails extensions. The full description of new features is here.
Best way how to start is to download pre-built IDE (inluding Mac friendly packaging) from NBExtras and give it a try. I was quite impressed. On modern hardware, the IDE is very responsive and Ruby development in Netbeans is even more fun as usual. The only small annoyance is frequent redraws and "flicker" of GUI when running on Windows - but it is likely one of the issues that may go away in final release.