SystemTray.isSupported returns false on Gnome Classic.
However, the System Tray is present and other applications can add/remove icons to it.

It is not clear why SystemTray.isSupported returns false, as the System Tray is there and is working.

Steps, to reproduce:
1) Login to Ubuntu choosing Gnome Classic graphical shell. (We used Ubuntu 12.04. Howeevr, the issue has also been seen on older versions)
2) Run the attached java program (the program just calls SystemTray.isSupported() and prints the result)
3) The program prints SystemTray is NOT supported

(If you login choosing Unity graphical shell, then the program prints SystemTray is supported and the tests pass).