Marlene Wagman-Geller's Once Again to Zelda: The Stories Behind Literature's Most Intriguing Dedications (Perigree/Penguin, 2008) is a series of forty-nine short essays (most under five pages or so) providing "the rest of the story" about modern book dedications (I say modern because she begins with Mary Shelley's dedication in Frankenstein, and only the first seven of the essays pertain to books published in the 19th century, while nine cover books published in the first few years of the current century).
It's an interesting concept, but since this is obviously a selection of dedications, it's easy to quibble with the choices the author chose. Many of those covered are hardly intriguing in any meaningful sense of the term (some are, but the vast majority of dedications to spouses and lovers are fairly conventional, even if the relationships themselves might have been anything but).
While this book could have stood for another round of editing, for very quick, rather formulaic introductions to various works of literature and those to whom they're dedicated, it will do fine (particularly if your interests run to modern literature). If you are expecting more, you may be disappointed.