Excellent: official Java support for system tray functionality
This is excellent! I use a very good 3rd party library to add system tray functionality to JFC Java applications when running under Windows and quietly fail when running on Linux. Sun's JDK 6.0 (Mustang) support covers Windows, KDE Linux, and Gnome Linux desktops in a portable way.
BTW, I do wish that Linux distribution creators and Sun could get together to have a JRE installed by default on Linux desktops, but I hold out little hope of this. GNU Java (Classpath, gcj, etc.) are coming along nicely but I find it much less facile to develop with than Sun's JDK.