Are you getting everything you want out of your run when you have music pumping through your head? I guess it is a personal preference of mine, but I don't run with my iPod. I love to run, not only because it is challenging, hard work, and generally good for my health, but also because of the mental perks it offers like: organizing my thoughts, working through tough situations in my mind, listening to my breathing to know I am working hard, etc...
There is too much clutter and overall noise when I throw on the headphones and try to get the same benefits from running. I don't hear my labored breath and my mind gets so overwhelmed by the music that the mental perks I get from running in silence just aren't there.
I understand that running, for some, is just a means to an end. A way to stay in shape, and just plain hard work. To me though, it is a release, a way to check your head, clear your thoughts, and work through anything you have on your mind one mile after the other.
So go run, with or without your iPod, and search for the mental perks that are waiting for you to cash in on. They are out there... You just might need to log a handful more miles before they show up... Especially if you have Justin Bieber playing in your ear.
If that is you, then that's a different mental issue altogether!