Interesting article on Active.com about the growing tension between runners attached to their MP3 players and race officials who increasingly are enforcing a relatively new ban on them.
I suspect more races will follow Portland's lead and market themselves as friendly to runners who want, or need, their own music on the course. I was startled by a statistic (perhaps accurate, perhaps hyperbolic) that 60-70% of race fields now contain runners using music as a motivator/tool. That means the vast majority of races include runners tuned in to playlists or podcasts!
iPod Conflict Brews in Racing