I love to run with music. I would say that in general I find it weird when running with a running partner since I miss my music. Races with no music allowed (there are some) I avoid.
For as long as I have run (and there have been reasonable devices) I have run with music. I even used to run with a Walkman but that truly sucked, lugging around that thing and switching the tape over part way through a run.
For yesterday's run I resurrected an old faithful podcast I used to listen to while training for the Ottawa Marathon's 1/2 Marathon in 2007. I have since used this podcast on and off for a great source of electronic music mixes that have the paces I desire for running.
The podcast is Podrunner.
A quick search will lead to lots of articles about running with music and how it can improve your performance by up to 15%. Like this these:
An important part of listening to music is to choose the correct BPM (Beats Per Minute) (See: Find The Right BPM for Your Perfect Running Playlist with This Chart). Research shows that an idea workout level is 120-140 BPM. Some articles just go with 130.
When I trained with the CBC Ottawa Gotta Run 2007 segment, our coach Rick Hellard, of Zone3sports, taught us the importance of running at 180 BPM. That is the rate of foot strike for top runners. They normally have a shorter stride than recreational runners and they hit the ground more frequently.
So, for me, when I am in running shape, I enjoy running at 180 BPM. Today's run at 180 BPM was maybe a little ambitious but I certainly got a good workout from it.
Try out Podrunner yourself for easy mixes at your desired BPM. I find they improve my runs and are a critical part of my training plan. Here I am talking about it in 2007 (Running Tunes).