So you want to file a bug against Nimbus? First, thank you very much! Jasper and I want Nimbus to be rock solid, and welcome all the bug reports we can get.
Bugs are filed in the same way as all other bugs in Swing: via bugs.sun.com. You can use this link to view current bugs. As you will see, all Nimbus bugs are prefixed either with Nimbus LAF or Nimbus L&F. Please continue this naming convention, as it helps us locate which bugs belong to Nimbus.
That's really all there is to it!