Hmm. I heard "Busk, busk" being sung by another singer at one of the clubs that I go to. It's one of my favourites. She also sang it far too slowly, in my opinion. Sounds like I should avoid singing it in that particular club and just sing it at the two others (she doesn't go to the others).

Is there any kind of etiquette at all? That if a singer sings a song regularly it is polite to leave it alone?

I do generally prefer not to tread on somebody else's song, but I have a few firm favourites.