Binary package hint: notify-osd
I identify myself as a Gnome user, but I use xmonad as the window manager for Gnome as it further increases my productivity. The window manager to be used with Gnome is defined with the environment variable WINDOW_MANAGER. I personally set this variable at the end of my ~/.profile by saying export WINDOW_MANAGER="/usr/bin/xmonad". A piece of software called gnome-wm then looks this variable up at start-up phase and runs the windows manager of my choice, or a default one in case I specified none.
Changing the value of the variable should have no effect on anything, but the window manager that gets started. With Jaunty however, setting the windows manager like this breaks the notification system. While debugging the problem I managed to get both my window manager and notification system working, by 1) unsetting the WINDOW_MANAGER variable 2) logging in with the variable unset 3) killing metacity window manager by hand 4) starting xmonad by hand.
Confirmed in both xmonad and awesome.