Judging a book by its cover

We've all heard the adage "don't judge a book by its cover". For those of you who haven't (have you grown up under a rock?) it's advocating judgment based on content merit, not aesthetic appeal. I understand that and often tell my students to keep this in mind when passing out copies of Catcher in the Rye, which they find entirely unappealing visually. The way a book looks does not correlate to how well it should be received creatively. 

However, one of my favourite aspects of literature and books in general is cover design. I'm a person who loves pretty things after all. When I walk into a book store, the books I'm drawn to have interesting, beautifully designed covers that catch my attention.  It's from this that I pick up the book and peruse the back cover to see what it's actually about. If the cover is boring, nothing in my mind entices me to stretch out my hand to pick up the book. For example: I recently purchased a copy of Anna Karenina by Leo Tolstoy but picked up the copy that looked like the cover to the left instead of the one on the right. I was drawn to the splash of colour, the photograph and the combination of different font faces. The other cover had dull colours and a painting which I did not connect with. For me, Anna Karenina is a tome. It will take me ages to read, but I want to accomplish this soon. If I have a copy of the book with a cover that appeals to me, I'm more likely to keep it close, and both see and think of it often, leading me to pick up and finish the book more quickly. Does anyone else look at cover design in that manner?

So this is my dilemma: in a world where aesthetic appeal drives the creation of the design of books, can we still honestly say we don't judge a book by its cover? If one aspect of our  buying decision is based on the appeal of its cover, we are making a judgment of some sort.

Another great example of modern cover design enhances the appeal of a novel is the new Penguin Essentials collection which I saw on Penguin UK's website. The novels in this collection are some of the twentieth-century’s most important books. When they were first published they changed the way we thought about literature and about life. And they have remained vital reading ever since. 

What is there not to love about this collection? The designs are unique and capture the essence of the heart of the book. The colours pop. And I want to be seen reading these in public (I really told you I was a hipster, didn't I?) 

So my question stands as this: what do you think about the phrase "Don't judge a book by its cover?"  How do you decide what book to purchase or what to leave on the shelf? It's an interesting debate.