I'm no expert on mp3 players, I don't even own one. But I bought my daughter an iPOD a while ago, and it's developing a significant advantage.

She bought a little hat for the iPOD that broadcasts an FM signal that is picked up by her car stereo. She puts her iPOD in random mode and creates her own radio station. The thing only cost $30 and she tells me it works like a charm.

If you own the market for a significant product category, your dominance creates its own advantage. You have everyone and his brother developing clever accessories. Ask Bill about this.