It seems I'm not alone in my attachment to my digital library. The Association of American Publishers reports that April 2009 showed a decrease in book sales in most categories except for ebooks, which jumped almost 230%, passing audiobook sales (which decreased) for the first time. The Dear Author blog post has an easier-to-read list showing how each category did. On a related note, Barron's is predicting that the Kindle will be a major revenue generator for Amazon, which unlike other eReader sellers makes money off the books as well as the devices.
I'm sure a lot of this downward trend for books is the economy. Books, especially hardcover books, are a discretionary expense. You can, after all, go to the library for the latest releases, or go to used bookstores or book-swaps for older books. But Kindle is doing well in this economy, so I think it's not all a matter of people tightening their belts. I think digital reading has turned a corner with the availability of eReaders that offer a pleasant, convenient, reading experience. I don't mean just Kindle and Sony dedicated eReaders; I think the iPhone/iTouch have had a huge impact on the sale of ebooks, too. Those screens are too small for me, but younger folks have better eyes.
It will be interesting to see if this ebook rising trend continues when the economy picks up (which we all hope will be soon).