Well, guest, I guess there are really lousy singers out there (some of whom become major c/w, rap, and rock stars), but when an activity is staffed by volunteers, isn't it to be expected that some of 'em won't be "professional?"  You expect musicians to play for nothing, and--surprise!--some of 'em suck!

You could try having each person have no more than 10 minutes on stage unless the audience clearly demands an encore.  Other than that, I really don't know how to hold a true "open mike" without allowing the lousy ones as much time as the enteraining acts.  Of course, you could restructure it as a "showcase" and require auditions, tapes, or prior knowledge of the person's work.

On the other hand, as Mark suggested, some of the good entertainers may have really sucked when they first started doing open mikes.  For one thing, stage fright can make you sing off key, forget lyrics, and play sloppily.  Nothing will get you used to performing in front of an audience except performing in front of an audience.

Also, if the lousy performer brings in a slew of buddies and they all order drinks, some pub owners may welcome them in preference to a better musician who comes in alone.

Genie