I am running NetBeans on Solaris and to be honest I don't like the default look and feel, mainly because of the sick-looking blue color. But it's very easy to change the look and feel. My favorite look and feel is
JGoodies Looks. To use a custom look and feel simply run NetBeans with the following parameters (for Looks):
./netbeans --cp:p /export/home/roumen/looks-2.1.2.jar --laf com.jgoodies.looks.plastic.PlasticXPLookAndFeel
If you want to change the look and feel pernamently, you can add it into etc/netbeans.conf. There is a parameter called netbeans_default_options. Add to this parameter string "--laf [LAF]", where [LAF] is the class representing the look and feel. Note that GTK LaF has improved a lot in JDK 6, so I also recommend trying GTK LaF if you run Linux or Solaris.
Here are screenshots to compare the default Solaris look & feel and JGoodies Looks:

NetBeans with default LaF on Solaris

NetBeans with JGoodies Looks LaF on Solaris
You can also edit your conf/netbeans.conf and add your laf line to the netbeans_default_options. Here is an example:
The JGoodies LaF isn't really supported. I was indeed able to change the color of the tabs by means of changing some UIManager values in an own module, but there is so much left that doesn't look good for me yet. The tabs, the toolbar and the editor selector icons have nothing to do with JGoodies. It's some kind of mix of Metal and WindowsClassic. I am sure the support for LaFs will be improved in the future.
I really would recommend running the GTK LaF. You can see a screen shot in my blog