Yeah, I've heard them used in folk metal, but the genre's not really my thing. I've always loved the sound of accordions in a rock band, taking the place of keyboards. I just recently joined an accordion-fronted band who play rock and punk covers and originals with the instrument at the forefront. It's absolutely ridiculous, sure, but I have to admit that I would have never guessed that "Blitzkrieg Bop" could sound so good coming from a squeezebox. 