So when I first saw this thread I suspected it wasn't really a question being asked, but rather another round of this:
http://www.metacafe.com/watch/hl-40044035/saturday_night_live_dana_carvey_as_grumpy_old_man_season_16/ Still, people have taken the time to try and offer a genuine explanation for what is purely a personal preference, so maybe I'll add. I like music when I run. My IPOD is about half country, about 25% 50-60s, and about 25% 90s music. If I'm plodding down a gravel road at about mile 3 and something up tempo comes on, like a Chuck Berry for instance, it causes me to kick my heels a little faster and push myself a little harder. It also helps a bit with keeping time. Most songs are around 3:30 so you can do rough math based on that.
Another good time for music is on a nice day, say late morning in late April when I'm driving cross country from a turkey hunt to a bowfishing spot. It's 75 degrees outside and there are no clouds to be seen. I love to roll the windows down in my truck, turn the radio up, and just enjoy being alive on the backroads of the midwest.
To each their own, as it should be.