I am reading the first chapter now (I recieved the book from Amazon yesterday), and already found the family tree useful, but then I usually don't mind spoilers (unless its a suspense story). When reading novels with many characters or those that span many years (Marquez's A Hundred Years of Solitude comes to mind) I often have to draw a family tree so as not to get lost. It's thoughtful of the publishers of the Oxford edition to save me the effort this time.