I do ride with an iPod sometimes and hear are the only conditions where I wear it:
- long ride on familiar road
- not much traffic on the road
- I keep only one headphone in my ear and it is the ear that is away from traffic
- I keep the volume really low (most of the time, I can’t hear the music over the wind noise)
- I have some kind of mirror so that I can see traffic behind me
So, those are the rules that I set for myself when I ride with an iPod. I don’t do it much, but I do it sometimes.