Regarding backing up and the content of the CD, not the physical disc. I also don't know if this is the same for music CD's. My Dad is head of Media for a Uni in the UK. He has a lot of software, all opbviously legal. Often, due to the high useage of the discs, his department either breaks them, they stop working due to scratches or they go missing. He rings the distributor or the manufacturer, gives them his details, and for a postage fee they send him new discs.
This is something he started doing q good few years ago, with his home discs. He would give them purchase details or send a cover sleeve, saying he paid for the use of the disc and content, not the physical disc, as is the wording on the copyright info more often than not. He often got and get's confused people on the end of the phone, but eventually he always wins.
I realise this is different for music, but again you are buying the right to play the music at home, not publically though, and I don't think that making copies is clear cut. Isn't it almost a licence? I am not saying this makes Music sharing right, if anything it is a little off topic, but we seem to be talking about backing up a fair bit too.
As for Music sharing, the legal stuff needs to be sorted out and then maybe the illegal stuff will decline. In the UK we don't have so much choice. I download music, but I also buy a lot more CD's than I have ever done, mainly because when I was unsure of an artist before I would go with my cautious side and save the cash, now I try them out, and if I like them I buy them. Not saying it's right, it's just what I do, but I don't share.
Marc