slight correction, there's no pedal express san francisco, but I've been a worker/owner at http://www.pedalexpess.com/berkeley for a couple years. We pay ourselves well (for the industry), have great benefits, and still manage to get the work done and make money. Takes a good group of people though. If you have it, I say dump the bosses off your back.

Cupid in SF (as mentioned above) is also a coop. Drag racer in SF is technically a coop, but is super small now and doesn't really qualify. IMHO, it's the only financial structure that can ultimately succeed in this industry.

If you want more info on bike messenger coop stuff, pm me and I'll be glad to talk your ear off.