Lol, I have been curious about this topic too-- as I've just started cycling. Personally I decided that I didn't feel safe enough. But if someone wants to ride with headphones-- I won't tell them stop. I may choose not to ride so closely though, lol.

I had to share this 'sighting' with you ladies though (As I said, I'm a newbie, so if this is usual my apologies): On a weekly ride that I do, typically 50+ people go. It's a blast-- you meet lots of people, etc. The last two rides-- there's a guy hauling one of those baby trailer deals-- with a stereo/boombox in it! I think it's pretty funny-- but I definitely don't complain when I hear the strains of a cool song drifting my way

cheers!