I guess I'm old fashioned....if some-one is known for singing a particular song, then I believe that other singers should steer clear of it in that club or session. By all means sing it elsewhere...but not there!

There's nothing better than folks joining in with the chorus of your song, but I think you should warn people if you are not doing standard verses as, of course, they will want to join in those too. Especially if they are favourites. This is, after all, how people learn new song...by osmosis!

By and large I would discourage joining in with instruments, but there is an exception to every rule. At a recent gig a member of the audience quietly started to join in with a harmonica. It sounded great!

Best wishes,

Peter