These aren’t coming particularly thick or fast, but don’t complain, they’re free.

This idea is more of an extension of another idea I read about not so long ago…. Well its probably quite long ago now, I’ve been procrastinating. Anyway one of the more recent mobile phone gimmicks is to add a pedometer to the phone, for exercise purposes. And an idea that was mooted quite a while ago (although as I understand it nothing’s yet come of it) was to use the pedometer to synchronise the beat of the music you’re listening to to the pound of your steps. I’m leaping to the assumption that you’d only enable this when jogging or running.
So here’s my idea, into this system add compatibility with the heart rate monitor strap things you can get (Polar is I believe one make).
Then use the heart rate to slowly drift the speed of the music (that is going at your running pace) to either increase or decrease your rate of work.

So in practice, you’d be running along, your music would be in time with your steps, and it would slowly increase in BPM and if the drift is timed well, you’d speed up. Your pace would be almost subliminally controlled like this to ensure that your heart rate is kept in a good exercise zone.