I guess I'm a follower allonger. It really depends on what the predominant mood is as to whether I feel it's OK to join in or to clap or whatever. I'd never initiate singing along (unless I actually knew the singer's feeling on that) but I will join in if everyone else seems to be doing it! I guess what can happen is that one set of people in one group or club's culture forment a 'norm' for them, but that doesn't always translate well to other environs?