I couldn't tell if this was a dup or not. And rather than make my own estimate of that, I'll let someone more experienced mark it as a dup if so.
So I've been running karmic, and 'at some point in the past few weeks' audio has stopped working. Sorry I can't pin time down more than that. My system is mostly up-to-date, but it certainly has the latest pulseaudio (0.9.16).
Everything seems to think it's playing fine, but no sound comes out. Nothing seems muted.
USER PID ACCESS COMMAND
/dev/snd/controlC0: mike 3548 F.... pulseaudio
Card hw:0 'Intel'/'HDA Intel at 0xfe9fc000 irq 21'
Mixer name : 'SigmaTel STAC9228'
Components : 'HDA:83847616,102801f3,00100201 HDA:14f12c06,14f1000f,00100000'
Controls : 29
Simple ctrls : 19
Date: Mon Aug 10 14:15:50 2009
DistroRelease: Ubuntu 9.10
Package: alsa-base 1.0.20+dfsg-1ubuntu4
ProcVersionSignature: Ubuntu 2.6.31-5.24-generic
Uname: Linux 2.6.31-5-generic i686