My system is a F12 with some packages from rawhide.
I noticed that when I update glibc to 2.11.90-4, libpulse no longer works.
(When I downgrade back to glibc 2.11 or 2.11.1, the problems disappear.)

With mplayer -ao pulse, I get the following message:
Assertion 'pthread_mutex_unlock(&m->mutex) == 0' failed at pulsecore/mutex-posix.c:108, function pa_mutex_unlock(). Aborting.

... and mplayer halts.

I also observe hangs pf firefox and metacity cause by this.

Staring at some back traces, I guess it might be something with threading, inbetween libpulse and pthreads.

I can reproduce the bug reliably on my i686 Thinkpad.
I spent a few days tracing it down, but I got to a point where I cannot continue without any advice...

Versions of packages:
glibc-common-2.11.90-4.i686
glibc-devel-2.11.90-4.i686
glibc-2.11.90-4.i686
glibc-headers-2.11.90-4.i686
nspr-4.8.2-1.fc12.i686
pulseaudio-0.9.21-2.fc12.i686
pulseaudio-libs-0.9.21-2.fc12.i686
pulseaudio-libs-glib2-0.9.21-2.fc12.i686
libcanberra-0.22-1.fc12.i686
libcanberra-gtk2-0.22-1.fc12.i686

alsa-utils-1.0.21-2.fc12.i686
alsa-lib-1.0.22-1.fc12.i686
( no other alsa* packages installed )