Switching Master and PCM
From this post on linuxquestions.org comes a workaround for situations whereby adjusting the Master Volume on some Intel sound cards doesn't actually have any effect on the volume. This is particularly annoying where you have a keyboard shortcut to change volume that does nothing more than put a pretty volume-changing graphic on the screen with no other noticeable effects (it's the PCM that will actually change the volume).
The post suggests putting the following line in the /etc/modprobe.conf file. I'm running Ubuntu Edgy at the moment and the relevant file there is /etc/modprobe.d/alsa-base
options snd_intel8x0 ac97_quirk=hp_only