Give the audience credit for knowing that when they come to an open mike they are attending a crap shoot. Most of the open mikes I have gone to, and the few that I have run, have provided enough pleasant surprises to counterbalance the horrors. Anyway, here in New York City, time is generally at a premium, and most open mikes allow everyone only 2 or at most 3 songs. (The open stages at the Postcrypt at Columbia University allow performers a 10-minute slot regarless of how many or few songs fit into it.) So the suffering is never so long as to drive anyone bonkers.

--- Steve