I have bought 61 books from the Sony Connect store (and not come across a badly formatted one yet - I must be lucky). Mainly Sci-Fi - Star Wars books account for almost half, Kim Stanley Robinson's Mars series, a bunch of Discworld books plus Lee Child's "Jack Reacher" novels, some Mario Puzo, Stephen Fry, and a couple of Stephen King (The Talisman and Black House)
I've bought 3 so far from Fictionwise (another half a dozen on my wish list)
I already have about half the books as paperback.