I installed xubuntu-desktop on a 12.04 Ubuntu upgrade after finding Gnome3 lacking. I've mostly been happy, but I've found an odd and frustrating bug. My laptop has two sound 'outputs' – an HDMI-out plug I never use, and the onboard speakers/headphones. For some reason, the hardware keys have been mapped to the HDMI output, even if I set it as 'fallback' in pavucontrol, and notify-osd only displays changes in the HDMI output (though the panel indicator volume control controls onboard sound). I'd ideally like both hardware keys and notify-osd to be looking at the onboard sound, though if I can't get notify-osd it's an acceptable loss. Having to click through a bunch of stuff to change volume is driving me crazy, though.
Googling suggested that it /may/ be a Pulseaudio/ALSA conflict, but the hardware keys seem to change at least indicated volume in pavucontrol for HDMI as expected (I don't have an HDMI cable to test actual sound output)