I am a voracious reader. I've been using a program called Palm Reader on various Palm OS devices for 5 or 6 years, for nearly all my reading needs. I can read books on my PDA way faster than a paper book, probably because I'm so accustomed to it. The only thing it's not good for is heavily annotated books like War and Peace (which I am reading right now in paper form) with all the French-English translations in the footnotes.
Reading on a small hand-held device (currently a Palm 755p) is far superior most of the time. It provides its own illumination for night reading, it's smaller and lighter than a book, and I can store hundreds (or more) of books on it at once. The only people it would be bad for are those with poor eyesight.
As for where I get all my ebooks, that's a discussion for a different thread.