Mountain biking this morning I came across two headphoned accidents-waiting-to-happen. The first was a runner trudging along in the middle of the singletrack. The second was a fellow mountain biker. Each time, I came up behind them and said "hello, passing". No response. So I waited for a few seconds and then noticed the talisman of modern day obliviousness - white headphone cables running up the side of their heads - but fortunately, I managed to get around the idiots at wide spots in the trail.
Wearing headphones when you're out cycling or running is dangerous and just plain stupid. If you have any interest in staying safe and being courteous to your fellow riders and joggers, leave the iPod at home. I don't care how much you like listening to California Gurls while you workout. The sounds of nature are far superior to Katy Perry's computer-tuned voice. If you don't think so, then there is no point in your being outside. Stay inside where you can safely workout and listen to music at the same time.