Fedora updated my Netbeans install last night and I had to set the look and feel in the config file again. Since this happened a few times and I never remember the laf option I thought I would write it down. Especially since the default Netbeans look and feel seems very ugly to me.
To change the laf to GTK add "--laf com.sun.java.swing.plaf.gtk.GTKLookAndFeel" to the netbeans_default_options in the netbeans.conf file. The netbeans.conf file is located in /usr/share/netbeans in the etc subdirectory of the netbeans version you are running.