I'm a book junkie and I make no bones about it. I'm counting on my Kindle to allow me to retain more books in my "Permanent Collection" than I could keep as paper books. But, the majority of my books are on back-up media, not on the Kindle itself. I'm paranoid about losing my data, so it's backed up 3 levels -- not only my eBooks, but my digital scrapbooking supplies, photos, and e-mail archives!
The MP3 story is quite different. A couple of Christmases ago, my hubby gave me a video iPod, so I used iTunes to put 3 or 4 of my favorite albums on the iPod. Hubby kept encouraging me to put more on it, but I didn't want to take the time and I was happy enough with what was there. (After all, each car had a 12-CD changer with MP3s on each disk, and there was a stack of additional MP3 CDs ready to go into the single CD slot.) Comes a time in early March and I had a business trip out of town. I returned to discover that my iPod now had 450 albums on it and hubby had built 4 or 5 custom playlists. We now refer to the iPod as "Dad's iPod'!
What I *would* be interested in, however, is putting an audible book (unabridged only) onto a portable device such as the iPod or my Kindle. I know the Kindle will play MP3s, but I haven't figured out if I can create a playlist to make sure that the tracks get played in the right sequence.