ZDTV OK, lets get the downside over with first. MP3 audio sounds noticeably worse than your CDs. The current crop of players only hold about an hour of music at the most. And the recording industry is doing everything it can to kill the MP3.
Lets start with portability.
They're so tiny, they fit just about anywhere. They're shockproof too. Jog, dance, hurl or bungee jump, the music just doesn't skip. Solid state storage makes for great portable music. And battery life is also great.