If you are a look and feel freak like me, you will notice that the toolbar is not just right under OS X 10.5, when running with default java 1.6, which is "1.6.0_13". The toolbar does not appear as "unified" and it will sooner or later turn out in to an eye-sore.
The way to work around this is to edit your netbeans.conf and tell netbeans to use JDK 1.5 instead of 1.6 for running. Put the following lines in to netbeans.conf (Probably at /Applications/NetBeans/NetBeans\ 6.7.app/Contents/Resources/NetBeans/etc/netbeans.conf)
netbeans_jdkhome="/System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Home/"
This will use your 1.5 version of Java, and it gives the right Unified toolbar look to netbeans. You can always set project specific JDK for each project in Netbeans.
So, here are couple of screen shots for comparisons.
1) Running with Jdk 1.6, non-unified
2) Running with Jdk 1.5, unified
If you don't want to edit the netbeans.conf file, just set your default java preference using "Java preferences" dialog in OS X. Select Java SE 5 as your default application Java, and you are all set.