1) The nature of the experience. With mass media, you watch, but with personal media, you participate.
2) The location. Mass media came into our living rooms, but you carry personal media with you everywhere you go.
3) the nature of the dominant players. Mass media was the world of the few and the large - the big Hollywoods producers, the big TV networks, and the widely circulated newspaper and magazines - but the personal media world is dominated by the many and the small.