Rule, it sounds like you're doing stuff with ALSA. Doesn't Ubuntu >= 8.10 use PulseAudio?
I've had problems with PulseAudio before, but it always seems like it worked after a fresh install. Sometimes it randomly stops working, and I have to restart pulse. Maybe you should restrict your search to things dealing with PulseAudio? I think you can also fiddle with what sound device you're using. If it really is ALSA, maybe try switching to PulseAudio?