There's a long history (going back to at least "Rock Around the Clock") of single B-sides becoming unexpected hits. Searching for the phrase "started playing the B-side" brings up several examples:
My favourite is the story of "Amen Brother", a forgettable (?) b-side instrumental by sixties funk band The Winstons that just happened to feature a really sweet break beat ... which went on to spawn an entire musical genre.
http://duckduckgo.com/?q=%22started+playing+the+b-side%22
http://www.google.com/search?q=%22started+playing+the+b-side...