Let's Talk Ugly Book Covers
They say don't judge a book by it's cover (whoever they are), but a beautiful cover, or at least a strategically designed one, can be a huge factor in whether or not a book gets picked up by a new reader.
Picture this: You're browsing. You want a particular book, and that's the reason that you've come into the bookstore, but you think, "Hey, I'm here, I might as well see what else is out." You're pretty much going to pick something up or not pick something up just based on what it looks like, aren't you? The cover is the precursor to getting you to read the blurb. If you've got a wonderful cover and a fantastic blurb that fills your potential reader with a burning question that OH MY GOD I MUST READ THIS BOOK AND FIND OUT WHAT HAPPENS then hey presto, you've probably just made a sale. Unless that person is using the bookshop as a showroom, but that's a different issue entirely.
Covers can also be extremely important for new authors. Certain genres will have set styles, for example historical romance ala Kate Morton mostly feature soft portrait style close ups of women's face with cursive writing. So if your book is marketed at people who like Kate Morton novels, then it's really easy to attract those people by having a cover that follows that sort of style. Some examples:
This is the cover you see on Goodreads: