I know I am... With the arrival of PulseAudio to join OSS, ALSA, GStreamer, aRts, ESOUND, NAS, Phonon etc etc it's a bit hard to see any clarity. A linux.com article clears up things a bit.
I seems to me the "standard" way for Gnome will probably be:
- Applications decode/generate audio using GStreamer
- GStreamer sends the audio to PulseAudio which performs volume control and routing
- ALSA drivers play the routed audio onto physical cards
All three projects have some overlap and do not require any of the others to work. OSS was replaced by ALSA. ESOUND was replaced by PulseAudio.
KDE is also using Phonon as a fourth layer for API stability and to allow applications an easy way to play sounds.