I was having major issues getting the audio to come out of my logitech headset. It got to be strange when the problem occured on both my laptop and desktop macs. I little search took me to 'macosxhints'. "Opening Audio Midi Setup and toggling from '2ch-16bit' to '1ch-16bit' (pausing to adjust the volume to cause it to make noise, just because) and then back to '2ch-16bit' seems to make it work consistently."

I was relieved and please that this seems to have resolved the issue.