I remember seeing a demo of their UIs when they gave an infosession at school. They look nothing like Swing--as far as I could tell, all the widgets were either custom or redesigned. If I remember correctly, it looked more like MS Office 2007 than anything else.

Since Swing is "lightweight"--all the widgets are drawn in Java instead of using native ones--using it to make a completely custom UI makes sense.

It is pretty common for enterprise desktop applications.

It is one of the few viable cross-platform desktop app frameworks.