To touch on Gregory's point - our decision on how to avoid contention between users is basically to ignore it. :) We'll have to let them work it out among themselves, except in the most extreme cases. I don't know what else to do; we don't have time to be babysitters for this, but the need for it is great enough that we felt we had to do something. I'm tired of writing back to people telling them we can't help them!
