The matisse problem in GUI development... 📎
So the challenge is here to make your UIs looking unfinished in the first iterations :-). With Swing it is not a big problem. You can very easily change the look and feel. In the first iterations you should use the napkin look and feel (you can use the following system property to change the Look And Feel without recompiling the application: -Dswing.defaultlaf=net.sourceforge.napkinlaf.NapkinLookAndFeel).
In the last iterations you could switch then to something like Substance.
Netbeans 6.0m2 is a Swing application in the early iterations, so with napkin it should look like these screenshots (1 or 2) :-).