Comment 8 for bug 392533

moomex, what kind of hardware and brand (laptop, desktop, netbook) do you have? It could be that your system does short-circuit something in lower parts of the library stack, not exposing brightness changes to HAL, which gnome-power-manager uses to obtain info about any changes you make via these special keys. Thus causing no notification-bubbles to show up, because they are simply not issued by gnome-power-manager.