For convenience and quality, I still don't think anything comes close to CDs. It seems like the major benefit for buying MP3s is that you can buy them track-by-track, except for certain albums where you're locked into buying the whole thing if you want it. For the people who want specific tracks from artists, downloads would probably be the way to go. For anyone buying full albums, I don't see why they would go this way instead of normal CD. But who knows, maybe this format will surprise us.