[xmonad] notify-send not showing any box when run

I am running with xmonad 0.8-1 on Ubuntu 8.10, integrating with the Gnome module My configuration is quite simple http://pastie.org/453213 - I haven't really grasped the Haskell syntax yet, so the configuration above has been "learning by example". I have one annoying problem: When running Ruby autotests, the test-program always ends its test-run with a message in the corner of my screen - this is done, using Gnome's "notify-send" command. But after switching to xmonad, I have not been able to get anything shown with "notify-send". Can anyone help me? Should I change something in my xmonad config or am I to use another command instead of "notify-send"? Kind regards, Carsten