Books are for everyone and it should stay like that making it a pay service in this case I think will discourage users.
It would be better to have VIP accounts or something along the lines.
Yes, that's exactly what I am going to do.
It sounds like Google Books. You can store your books on different "shelves" like "To read" "reading" "have read" and "favorites". I don't think I would pay for a service like that when they are plentiful all over the net.
Well, not quite like Google Books, but has something in common, yes. As far as I understand, Google Books primarily concerns with providing content of books or at least extracts from content. You indeed can store books on different shelves, but as far as I grasp, you can choose the books only from existing set, you can't add your own book to Google Books (or I am not right?).
My service is going to develop more toward the direction of librarything
(the last is for movies, not books, but the concept is the point). Both these services have free ordinary accounts and also paid VIP accounts with some additional content/functionality. And that's axactly what I am going to do with my service, so the basic functionality would be free. So, you wouldn't need to pay for something what is all over the internet. Anyway, at the moment my service is completely free for everyone!