I totally know what Shifter's talking about. I'm going through the same thing with books. I got an e-reader a few months ago (yeah, no, not a Kindle, and not a sexy new Kindle, but a Bookeen Opus, which is the smallest and lightest e-reader on the market, and yes, I like it, but I'm tired of explaining to random people in airports and restaurants that not all e-readers are Kindles). My dream would be to have only a few physical books--the ones by my favorite writers, the ones I pick up and look through occasionally, and the ones that are autographed. So I started looking through my books and really being honest with myself. Which ones might I read again? Which ones have I not opened in ten years?
It's been an interesting experience. On the one hand, I'm a former English major, so a lot of my stuff is readily available for e-readers, and it's free. The collected works of Charles Dickens are easy to come by. Even the collected works of Wilkie Collins aren't difficult to find. On the other hand, there's a lot that isn't available yet. I have some academic texts that I really enjoy. Some of my absolute favorite books, my touchstone books, are not yet available as e-books (Marathon Man is one I'm particularly sad about--I'd feel great about having that book in my purse all the time).
Some things are actively better as e-books. When I bought the collected letters of Elizabeth Barrett and Robert Browning (from before she was Barrett-Browning), I could not afford a nice edition. A good edition reproduces certain pages of the letters, and has footnotes providing context for some of the things they mention. I was really fond of Browning's doodles--there's a cute one where he draws a musical note in the margin to describe the squeaky wheel sound that grates on his nerves when he has a migraine, for instance. Not knowing that it's there makes the letter kind of whiny, but the doodle hints at a lively humor. The edition that I had was pretty much your bargain basement text, with no footnotes and no facsimiles. So far I've only been able to replace volume 1, but there's a nice PDF with the pages I remember and nice footnotes.
I have six boxes of books ready to go to a charity. A couple of other boxes are waiting to be mailed out to friends and family, but I'm still replacing a few special titles. I'm really hoping that I can get down to one bookshelf (which would mean getting rid of about 3/4 of my collection). No doubt some tough choices lie ahead...