I just tested QT Jambi. It is cool of QT widgets in Java. I like it. And it is very fast and the QT Designer is good but not as good as WindowBuilder Pro‘s SWT Designer, IMO.
But there is a nasty bug for QT Jambi integration with Eclipse. QT Jambi will add a com.trolltech.qtjambi.juicBuilder to each projects in my workspace. And these modifications will mark all of my projects as SVN modified. I have to disable it and restore all my .project files! This bug is really nasty!