I just installed JProbe Profiler which is written in Swing and boy does it look bad. The UI is typical Swing using the Metal L&F and just looks awful. It grates on my eyes. The interesting thing is that I use Intellij as my IDE and it looks very nice because they took the time to create their own look and feel and do things right.
It is very clear that an app that looks like JProbe would never sell to non-developers and this is why Java has lost the battle for the desktop. It is difficult to create a nice looking UI. The average Swing programmer will create something that looks like JProbe which is really ugly mainly because of the Metal L&F (even Intellij doesn't look great with the Metal L&F).