My local club is what this thread terms a concert club, in that we have guests of pretty high quality almost every week, with one floor spot first for the more regular club singers. As a non-performer this suits me fine, but I can see who some might find it constricting. However there are other local clubs with different policies, and there doesn't seem to be any complaints on the "joining in on the choruses" front.   As my wife and daughter have developed as performers through floor spots here, the club can't be totally useless in that respect, either.

The main problem I see with Singers nights is that the non-regular performers wait to do their spot and then bugger off: I think that selfish and disrespectful. I don't think that this adds a lot to the value of the club or the folk movement.