Apple is likely to face increasingly stiff competition from other online music stores and from other makers of MP3 players. Its lead is not impregnable. But the iPod and iTunes have already begun to redefine the basic unit of music consumption. It used to be the CD. Now it is the song. Soon it will be the playlist, a personalized mix of musical tracks.
The iTunes Music Store already sells celebrity playlists — like a clutch of songs chosen, say, by Tom Petty or Sheryl Crow. And the new version of the iTunes software introduced this week offers users the chance to publish their own playlists seamlessly. We are entering a world of collective eclecticism, in which music lovers can guide one another into the hidden recesses of the library of recorded music.