I walked along the road for about twenty minutes until I could flag down a ride into town. It was an old, wrinkly transport pilot that gave me a cigar. He played loud music through the system. It was a bassy random that the system had come up with to suit his mood. It thundered along with a beat faster than I could run. It was just loud and rough enough to suit my mood too.
I have always thought the idea of a music service that knew your mood and could adjust what's playing to suit your tastes would be a top seller in today's self-possessed world. As far as I know, they haven't yet come up with publicly available technology that will actually generate music for you, nor technology that can accurately assess your mood (hook your MP3 player up to your galvanometer, anyone?).
What I have found, however, are some very interesting offerings that allow you to create a radio station, commercial free, that will play random music based on a list of your current favorite artists. This music service, called Rhapsody, is free for Comcast cable internet customers.
Here's an example: I wanted a little raging instrumental guitar rock to listen to while cranking out some emails. I entered in only three names: Joe Satriani, Eric Johnson, and Steve Morse. It then treated me to a variety of songs that were somehow related to these, many of which were not written by any of these authors. And, true to my hopes, it produced songs that had one major thing in common: excellent guitar.
Incidentally, while I was trying to figure out some other authors I could plug in, I found another amazing site which helps with exactly this. Called Music-Map, this site allows you to trace threads of commonality between artists and find others who are related. What a great tool (and a great marketing tool to get more money out of my wallet...)