I have recently started trail running, and spend at least 3 days a week on the local trails. Fortunately, I'm usually there during lunch and don't come across many other people on the trails.
When I used to walk or run on the street or sidewalk, I would often take my iPod with me. I felt ok wearing them in that setting because the sidewalks were wide enough where if anyone needed to pass, they could easily do so. If I was on the street, I would generally be facing oncoming traffic and would see any vehicles coming at me, giving me plenty of time to avoid them.
My first time on the trail, I brought my iPod along, but quickly realized that the trail was very narrow and oncoming traffic was obstructed by the vegetation and growth along the trail. Additionally, I would not be able to hear anyone coming from behind me, and they would probably not see me until they were right on top of me. Because this is a multi-use trail, hiking and biking, I felt very uncomfortable wearing my iPod and not being atuned to my surroundings.
Why write this? I've seen a lot of posts on this topic. Most deal more with the eco reasons for not wearing an iPod. Don't you want to hear wildlife on the trail? Do you want to miss out on the peacefulness of being one with nature? I, too, feel that while in nature, you should avoid wearing the iPod. But trail running in the city doesn't hold the same aesthetically pleasing surroundings that the Grand Tetons do, so I'm ok with it from that perspective.
My issue is more a safety issue. Since my first run, I've left the iPod at home when going on the mixed-use trails for my safety and the safety of others on the trail. Today, on my run, I quickly came around a bend and came nearly face-to-face with a person talking on their cell phone. They were totally oblivious to me coming. I heard them, but they didn't hear me. I thought they were going to have a heart attack.
This didn't have much of a chance of causing much damage to myself or the other person, but had one, or both of us been on a bike and not heard the other one coming, it could have been extremely dangerous. So, for safety sake, please leave the distractions at home when on any narrow, mixed use trails. Always be on the look out and listen for others coming.