This question came up over on the FSM boards, and I actually found it interesting, so I'll post it here.
You buy a CD. Some time later, it doesn't matter how long, you rip the CD to your computer's hard drive for your own personal use, either to burn a new copy to use in the car or to put on your MP3 player or to listen using your computer speakers or whatever. Some time after that, for whatever reason, you decide to sell the original CD.
Should you then delete the ripped music files from your computer?