I do it all the time. I did it last weekend when I bought The Island. I did it in a Borders once and came home with a copy of Naked simply because the cover was funny. Sure, we shouldn't judge people by their "covers," but judging books by their covers is a tried and true way to pick out a new book!
For example, after my dear friend Trixie noticed me reading The Island, she lent me two more books by Elin Hilderbrand and two by Marisa de los Santos. All of the book jackets are beautiful. If these images don't make you want to read, I don't know what will. Well, okay, yes, the book jacket descriptions are certainly captivating, but book covers exist for a reason.
Silver Girl, by Elin Hilderbrand
To my delight, Hilderbrand continues the beach themed book covers. I finished The Love Season yesterday and it did not disappoint. I was worried, after loving The Island so much that I had built Hilderbrand up in my head too much and that perhaps the first novel was just a flash in the pan. Thankfully, my concerns were unfounded and The Love Season was more than wonderful. This book portrays, very eloquently, how your life can change in just one day, or over the course of many, many years.
I have never read Marisa de los Santos, but if her book covers are any indication, I will love her too. This cover speaks to me in so many ways. There are multiple pairs of boots in varying sizes, leading me to believe the book is about a family, probably narrated (narr-i-ated if you're my husband) by the mother.
This one looks great too! The inside flap of the book jacket is certainly more descriptive, but once you read it the cover makes more sense.
So when it comes to picking books, ignore your Grandmother's advice and judge a book by its cover. Someone, somewhere, in some marketing office designed that cover to draw you and and grab your attention. If it worked, all the better! You could discover a new favorite author.