What interested me was the option to read the book online for FREE. I don't have any devices to read books on, except my computer, so I really have no need to download the books. How much online reading will I actually do? I don't know, but it's kind of fun to play with. You can choose book or document format, choose your font and font size, and even add bookmarks to the books you're reading, so you can find your place later. It even keeps a list of the books you've looked at recently. It might just be a good way to check out a book I'm thinking about reading, before I request it from the library.
I also want to check out Read Print. It doesn't have the new books, but there are a lot of books available - a lot of classics, which I almost hate to admit that I've never read. I guess I have no excuse now, except for the usual 'So many books, so little time' that I always use.