Speaking as a bride who is getting married in less than two months, who has received a fair share of stuff that was off registry. It’s a 90% shot that book will never get touched EVER, until it’s garage saled. Get something off the registry, or send a check. It’s either something the couple decided together that they wanted (registry) or it’s something they need (money).
While I understand the idea, and think it’s great that you want to do the book thing, chances are the couple (if they are anything like me, my fiance and my friends) is VERY busy with a combination of, or all of the following : house hunting, work, school, planning the wedding, navigating new family waters, going to friends weddings, being in other friends weddings, and occasionally sleeping.
Also, unless you know the couple VERY well and you have been to their homes, don’t go off registry, don’t buy them art. I have 2 pottery vases that are some of the fugliest things I have ever seen in my life and a painting that can only be loved by the artist and his or her mother. While I am grateful that the people who purchased the items took time out of their busy lives to purchase something for me, and I am grateful they came to the shower, I feel bad that they wasted their hard earned money on stuff I wouldn’t give to someone I disliked intensely. I am currently comtemplating ways to destroy the vases (or at least find alternative uses for, ashtrays? loose change holders? weapons in case we ever get broken into?) , and trying to decide if the oil paint will hinder or enhance a bonfire, of course I could always submit it to the Museum of Bad Art…