I often do judge a book by its cover. So many books are flung onto the porch every week for the show. On the way to the kitchen, I open the (usually) padded envelope and look at the cover of the book. I don't much care whether it's hard cover or paperback, but I like a nice texture and color. If it's teal, turquoise, aqua, or sky blue, so much the better. I've been known to keep these, and make beautiful colored stacks, or organize by color. The author's photo either compels me or doesn't. If the author looks bratty, or arrogant, the book goes in the reject pile. Not that the author has to look friendly, either. He or she just has to look ... interesting and approachable. I can't think of any author worth spending time on the phone with if they're not nice or fun or glad to be there.
Apparently, a lot of people judge books by their covers. Others judge books by their covers, too.