I don't listen to anything other than the sounds around me when I ride (and when I used to run).

As a woman riding / running alone, I feel a very strong need to be aware of what's going on around me at all times. Much like body posture dictating whether I look confident or vulnerable (an easy target), sporting headphones/ear buds (one or two), gives off an air of vulnerability, regardless of how much you can or cannot hear.