I've been using NetBeans 6.5 for some time with Nimbus laf that came with Java 6u10. I have to say I like Nimbus, I am using it and not going to switch back to Metal or Windows. BTW I've always liked the former more, because of good looking toolbar and editor tabs. Anyway, there are two things, for now at least, that annoy me in NetBeans working under Nimbus (I believe these are NetBeans issues) - the colors of editor tabs and their inconsistence and ugly usage of border around editor pane. Look at the picture below.
Hopefully the selected tab will get less saturated to make it less agressive and more readable for the eye and border at the top of editor pane will long enough to reach its ends :). It will make tabs look more natural, more finished. For now it seems like tabs are alien to the rest of the NetBeans ui. They look more like buttons, because of this line issue.
I know glitches I've mentioned will not make you scream in the middle of the night sweating, but refining those would please my aesthetic needs :). Of course I am not the only one pointing those issues. Just search for "nimbus tabs" in firstname.lastname@example.org mailing list and you would see polished look does matter to developers.