I ride with earbuds and listen to music. If I'm in a strange place or in very stressful traffic I'll take them out, but on my regular commute I wear them almost all the time. I can hear traffic, but not from as far away as without. I tried wearing just one but got disoriented.
I would never recommend wearing earbuds while riding to someone because of the distraction issue, but if you want to, you can teach yourself to ride safely with them, imo. But it takes a little thought and practice. Contrary to popular belief they do not cause you to swerve all over the place
Keep the volume low, ride in a straight line, assume you have someone on your tail ready to pass at all times and check your back regularly. I just play the same stuff over and over, and do not have a problem blocking it out if I need to concentrate on something unusual.
For the record, I have gotten a lot more distracted by riding with someone else and chatting than from the music I listen to everyday.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett