I’m not sure why, but sound output protocols just seem to be so schizoid in Debian builds (which include Ubuntu).

First, there’s JACK.
Then there’s OSS (Open Sound System).
Next is ALSA (Advanced Linux Sound Architecture).
Finally, the latest project is PulseAudio.

ALSA is pretty stable, but as it’s particular to Linux alone, some are more enthused about OSS. PulseAudio is supposed to be the latest and greatest as it addresses software mixing (more than one application/program has access to sound, by software means) better, but it has brought Ubuntu 8.04 to its knees.

I am not the only one who cannot get a microphone to work, much less the other goodies. PulseAudio is almost like a fickle yet jealous lover—it might work for you, it might not—but if you fiddle with it to get it to work, it can have adverse effects on your system (a good drubbing, perhaps?)