I'm in the absolutely no headphones camp. People who say they are fine and can hear everthing since they don't turn their headphones up very loud or wear one earbud belong in the same camp as those who drink and then say they are just fine to drive in my eyes. They don't understand how dangerous they are being.

Being on a trail is no excuse - its almost worse than being on the road - sure there is no car traffic, but trail use (at least to me) almost seems inherently more dangerous than road riding even without tons of folks off in their own little worlds. I don't even think that joggers/ skaters etc. who are on multi use trails should be allowed to use headphones.