Can you search for bits of text, or phrases to refind them with your Kindle?
You can on a Kindle, I have to assume you can on any of the others as well. I think they're a great way to read books that you don't really need to have (or care about having) on a shelf somewhere. That being said, there are still books I want to have on my shelf.
Funny though, the Kindle has had the same effect on my book reading that the first VCRs had on my movie watching. That is, I rarely watched movies before the VCR, but once I got one, I found myself not only renting tapes, but also going to the movie theater. On the Kindle I read books that I would never
drive to a book store to buy. Things I want to read, but I just wouldn't have bothered with before.