I think that a lot of problems could be solved by giving performers a set time for their act. In folk clubs it could be the same for everyone if you really wanted to be fair. I well remember frequently sitting through "3 songs" that each went for 10 minutes. Telling performers they can do x number of songs is a recipe for disaster, I reckon. It can become a real power trip. I always ask for a set time for myself and stick to it.
                           Joy-who-hates-to-leave-the-stage-too.