Mac OS X version 10.7.3 running on amd64
Java(TM) SE Runtime Environment (build 1.7.0_04-ea-b13)
Popup menus have no visible borders which would be distinguishing the popup menu from the background area. This is especially annoying with white popup on white background (e.g. in editor area in NetBeans IDE).
The bug is reproducible with in a plain Swing application (e.g. SwingSet demo).
Related NetBeans bug: