I agree with McGrath, folk music can be serious business, for example, one of my favourite songs to perform, "The Wife of Usher's Well" simply would not work if one's tongue is planted firmly in cheek. On the other hand a talkin' blues number or something of that ilk should be a bit more light-hearted. Personally, I think the most important thing is to be completely invested in the song you are performing, a ballad about death or lost love or something should not be performed with a wide grin. I agree though, that some "folksingers" take open mic night at the local pub far too seriously.