As I prepare to move, one thing I'm doing is selling all of my CDs. I have the music on my computer, and it's backed up to a hard drive, so what do I have to lose besides cover art? (A valid concern - for someone way more "into" music than I).
I've heard it said that our wholesale conversion to MP3s foreshadows a similar shift in the book world, but I have my doubts for two reasons.
One, people read more slowly on screen than on paper. This study suggests 10% slower, but it's up to 25% slower in other studies. Do I want to read 10% fewer books in a year? No.
Two, the conversion of existing media to digital format is much more difficult. A CD can be downloaded in the background, and Gracenote can enter your track names. How about scanning a book? ... hey, come back! I can see all the former grad students in humanities and social sciences running away as fast as they can. You have to scan each page one at a time, and, as Google has discovered, you can't make a high-quality copy without tearing apart the original book. That means no resale. The difference, of course, is that a CD was already a digital format. Imagine if the consumer-oriented MP3 had been invented during the cassette era.
The upshot is that even if people start buying mostly in digital formats, they're going to continue to buy, keep, and resell physical books for a while. There won't be any overnight shift to e-books.