Another Ubuntu upgrade, another sound configuration that doesn't work out of the box. This is what I had to do for Ubuntu 8.10, that also worked for this version:
$ sudo vim /etc/init.d/alsa-utils
Around line 364, replace this
[ "$TARGET_CARD" = "all" ] && log_action_end_msg_and_exit "$EXITSTATUS" exit $EXITSTATUS ;; stop) EXITSTATUS=0 TARGET_CARD="$2"
[ "$TARGET_CARD" = "all" ] && log_action_end_msg_and_exit "$EXITSTATUS" exit $EXITSTATUS ;; stop) ifconfig wlan0 down ifconfig eth0 down EXITSTATUS=0 TARGET_CARD="$2"
Then restart. In 9.04 I also had to go through my volume control panel and make sure nothing was turned all the way down or muted. I think I had to unmute the master volume and turn PCM Playback (under HDA Intel) up.
Please comment if this helps you!
UPDATE April 29th, 2009: I also had to reinstall flash in order to get sound working in Firefox again.