Barry Schultz would agree. However having earbuds in would probably bother me. When we are playing rec rounds I sometimes use my phone/mp3 player to quietly play some tunes that don't have lyrics (if the group doesnt mind).
I think music out on the course isn't so bad. I have a problem with the head phones, I think that is really distracts me. But it has to be good music, and if you are walking up on another group of golfers teeing off you should show them respect and turn your music off or down. Not everyone listens to the same music. There is nothing worse than this group at one of my local courses that walk around with some terrible rap music blasting. I don't want to hear that. Their rap music really bothers me to hear when I am teeing off and playing round of disc golf.
I usually just pick a song that I really like and listen to it before I hit the course, and have that song stuck in my head to jam with for the round.
A guy around here uses portable speakers. I cannot say if my game is any worse when we play, but I would not want it for a tourney. For casual play, it helps me remember disc golf is casual and should be played for fun all the time.
For headphones, try lacing em through the back. I personally prefer an iPhone. It isn't too loud and less hassle. Not only that, but with headphones I can't hear my surroundings. Unless it's ska, I'd prefer others turn their crappy music down or off;)