See David Pogue/NYTimes on Paying the Piper, Round 2: The Repertory Grows about the last year of music industry attempts to sell online, and efforts going forward. Same issues as always: price, convenience in user interface as well as with the product once you buy it (read: DRM restrictions) and selection.
Oh, and catch Ed Felten's look at a Washington Post article that talks about SunnComm and a copy-protected Anthony Hamilton CD which an Amazon reviewer noted had annoying DRM, and the reporter had trouble accurately describing: