I came across this video of a heavy metal concert in France on YouTube and it made me think of this thread. The song is one of the best known of the band (Rammstein) involved, and the lead singer encourages the the audience to just sing the chorus to him for large sections of the song. At one point he even sort of conducts.

My point is that it isn't just folk audiences who want to sing along if the know the song. People just like to sing along.

http://www.youtube.com/watch?v=fLp63WBV-Ic