From looking at the thread comments so far it would seem that experiences in various parts of the country differ.

I've found the problem with some open mikes is that they lack the sense of community of a folk club. People arrive with their fan club of five mates, do their bit, then talk loudly at the bar while other people are singing, and leave early.

There are a number of thriving folk clubs in our area where it is rare for anyone to leave before the end, and everyone encourages each other's performanace.

Obviously this might just be in our local area.