I have a Sony Reader (PRS-505) and I like it a lot.
I originally planned to buy a couple of books a month for it, but the Sony store has a lot of cheap books (and free ones too) and there are several other online retailers that sell compatible books.
I'm really surprised at the number of free books that I can get for it -- a lot of authors will put up one book of a series for free to entice you to buy the rest of them.
I haven't bought a new book in several months and my backlog of books to read is very long.
I've been reading longer books than I normally do because I don't have to carry a big heavy volume. Likewise, I can carry several smaller books at a time without having to juggle them. I'm reading three books right now and I can easily choose the one I want to read based on my mood, since I'm have them all together in my hand.
I may be slightly enthusiastic about my Reader.