SlotMusic cards look to replace CDs it appears as a means to purchase MP3 files in a physical form:
http://www.slotmusic.org/
I'm not interested. Why would I have my car stereo and home stereo replaced just so I can play some lower quality tracks using a completely new format?
Maybe in 10 years, but for now I'm happy buying CDs and music off iTunes.
It's interesting, but I think the idea of physical purchases of music is fading away.
What he said....
And to exand upon that, I can see downloads eventually giving way to wireless/internet distribution of music with devices like Slacker.com's G2 portable radio or similar apps for phones (which are rapidly becoming mp3 players with phone capabilities).