I buy CDs because I like the packaging, lyrics, artwork etc. I make an effort to take my CDs off the shelf and play them (even though I have an MP3 player).
However, there are times when I don't want to buy the CD, and perhaps just keep a few random songs or the album on MP3 format simply because it's not a "must have".
Put it down to having a fucken conscience or something, but I wouldn't mind rewarding the artist by compensating them somewhat (without the need for buying the CD).
That's how iTunes works now anyway. People buying random songs. I don't see why this is going to be restricted to the mainstream. It's just another channel to get your music legally without walking into a high street store or buying from a distro.
Meanwhile, people are downloading illegally anyway and never buying anything so everyone loses out. I'm suggesting a compromise knowing perfectly well people aren't going to buy CDs anymore.