What gives? I updated a few packages on my Fedora 9 Workstation and sound stops.
I tracked it down from an error message in the syslog. The error said that Pulseaudio was having an an error connecting to console-kit. I had not changed anything there, so I had to go digging. I found that it was related to pulse audio not getting started correctly when the x session started up. The ck-xinit-session was not executed in /etc/X11/xdm/Xsession.
Google told me others had a similar issue and there was a simple patch that I found in Redhat Bugzilla. It just adds one small change to the /etc/X11/xinit/Xsession file.
ck-xinit-session needed to start befor the PulseAudio daemon started. Pulseaudio website also comments on the startup issue.