I have most of my CDs ripped onto the computer as FLACs, which gets periodically synced to an external harddrive that is normally kept disconnected. Since I rarely use the original CDs (just keep them on the media shelves), I figure I'm pretty well covered as far as backups are concerned. Assuming all else being equal in the hardware chain, I don't believe in any inherent fidelity difference playing back from the original CD, a burned CD, or from the harddrive.