I'm in the "no headphones" camp as well. I've never done it; never will.

I lost the hearing in my right ear, nearly 30 years ago, when I crashed my bike. Even if I had hearing in both ears, I wouldn't do it, and I avoid cyclists that do. I fail to understand those that feel it does NOT impede their awareness around them.

When we should always strive to be as predictable as possible when cycling, I feel it has the potential to add an element of unpredicability that doesn't need to be there. Why not give yourself the best chance possible to be safe?

Food for thought...