I guess that what we are facing here are two different perspectives: the first from those for whom music is a "real" job, and the second from those who make money only occasionaly (at most) from music. I've been (and still am) on both sides, and (now that you make me think of it) I try to adopt somewhat different attitudes. In a non payed act, among other friends in a public place (a bar or a party), I tend not to care too much about other people taking the command of the situation, but when I am in a job, I'm careful about letting others interfere in the show. Sometimes the bar owner or the party organizer likes it, sometimes he doesn't. I try to antecipate what pleases him the most. It also depends on the moment. Normally a little bit of "singing together" can result great, if late in the show, but can be desastrous if the show-man is too soft and doesn't have an attitude that clearly sets the rules.

I'm not surprised to read the opinion of Dave and Scott. They are true professionals. In addition, it's also possible that latins (i'm portuguese and Andrea is italian, I think) tend to be more informal and expect that "intense participation" from the public is a normal and desirable situation.
José Matias.