As George has said, we all have clubs or nights that we find better or worse. I think this thread idea would be more useful to those of us in varied places, and probably more civil, if we could describe what makes a bad experience, and what makes a good experience, from the viewpoint of a performer or an audience member.
As an audience member (at concert-type clubs far more often than singaround type) I most object to cutting the guest short for any reason, the loud machines (espresso and frozen drink blenders), and, especially, loud talking, almost unavoidable when the bar is in the same room. It is discouraging when the 'regulars' of that performer talk; maybe they hear him often and are glad to get together, but I want to hear the performer! I also think it would be good if there were established expectations about when the audience sings along. If the performer asks us to join in a chorus, either well-known or taught then and there, great, I love singing together. But I go to hear the guest performer, and find it distracting, and detracting from the experience, if there are people who feel they must sing along with everything, including the verses or obvious solo type songs, and even when they do not even know the words and just 'aahh' along.