Don't you just hate that saying? Of course it's not literally just meant towards books, it is also used metaphorically, but lets just talk about books for now. I always always always judge a book by it's cover... being in the creative field, it's just instinct to be drawn to something aesthetically pleasing...and it has to look pretty on the bookshelf, doesn't it?
I have just finished reading 'The Thirteenth Tale' by Diane Setterfield and it was the cover that attracted me to it. (I got it for Christmas when I sent my boyfriend the entire contents of my Amazon basket.) I instantly knew that it would involve young twins, or sisters, and as the title contained 'thirteenth' which I associated with horror films and of course Friday the 13th, I knew it would probably be some sort of haunting tale about sisters, fantastic.
So the cover of a book will instantly determine whether it is to your taste or not and you could just about get a feel of the storyline without even having to read the back. Therefore, the saying is indeed complete nonsense.
I'm not going to say much about the book because I know I'll ruin it for anyone who wishes to read it, but it was an amazing book, and even though I am reading several other books at the same time, this was one that completely held my attention and I finished it very very quickly. I recommend it to all book lovers, and yes it was a haunting tale about twins, but you'll just have to read it to know what happened... which is a lot lot more than I am divulging!
(Of course, you do also get many books with front covers that have absolutely nothing to do with the storyline, but that's a whole other topic!)