So suddenly I see No volume control GStreamer plugins and/or devices
found instead of the usual volume control tool in Feisty. I googled
the problem and most of the solutions hinged around the system not
detecting the soundcard, or the user forgetting that they didn't have
one =) But my sound had been working fine for a few months, so it had to
be something else. In this case, careless use of the usermod command;
I used the command usermod -G groupname to add my user to a group I
had just created. Unfortunately it removed me from every other group,
including the audio group.
A quick gedit of /etc/group and I was back in business. The moral of the story: if your sound suddenly stops working, check that your user is still a member of the audio group. Oh, and use usermod more carefully than I did.