we've definitely had some issues with this. i think it helps to some degree that we are small and that we aren't an officially registered non-profit- we don't have bureaucracy, we have the monthly meeting.
we're all friends, we all see each other on a regular basis (outside of the bikeshop).
however, it also hurts us sometimes. we've had one former mechanic and one former volunteer in particular who had serious problems with un-called for aggression and violence in the community at large and in the shop. in both situations, in part because we are so small, collective members have been wary of confronting them...
we also lacked the mechanisms for supporting these people in addressing their problems, and now they're both moving to other communities (asheville, NC and St. petersburg, FL).
for the most part, we've survived pretty well by just setting the tone with our own behaviors.
i just wish we were able to do more than just boot people from the project, and that we had been faster to address these problems in the first place.