I really appreciate anyone who really makes an effort to make the spine apart of the design of a book. Now after dabbling in book design this summer, I understand how easy it is for the spine to become an after thought to the front and even back covers. But as many of you pointed out, the spine is most likely what readers will first see (if browsing through bookshelves as opposed to online venues) and serves a purpose of conveying information. Visually, it should be able to hold its own too!
I've pointed out before how much I admire beautifully crafted, detailed, and ornate book cover designs. I think the same applies to the spine as well. But a nice, clean simple design sometimes is the best solution and can be just as stunning. Whichever the case, as long as the spine is considered as part of the design and works together with the design as a whole, then it works.