When I run, I have to have music. I can feel the difference between running with music and running without. When I have my music on, I feel like nothing can stop me, like I am invincible. It's also a great way for me to 'tune' out the day and just relax to some good music. What did people do before the days of portable music?! Some may argue that running with music defeats the whole purpose of running: to take in the world around you, focus on your stride, to experience nature... but I think if music makes your workout more enjoyable, then why not plug in for some good tunes?
I came across this article today that talks about the pros and cons of running with music, and it discusses the heated debate between running with tunes and running without. There is a lot of talk out there about the correlation of music and running.