At the link above, Joe Wikert of Wiley shows two alternatives of the cover of a book called Blogging Heroes, and asks his readers which they prefer. I didn't like either. Well, the one with the man on it would have been OK if he'd had a better pair of knickers.
Do take a look. I think Joe needs some good advice if he wants the book to sell on the basis of its looks. He says it "features wisdom and wit from some of the world's most successful bloggers, how they got to the top of the rankings and recommendations they have for the rest of us."