Some years ago I read the novel London by Edward Rutherfurd. For them as don't know it, it's a fictional/historical novel that spans the entire 2000-year history of London, as seen through the eyes of five fictional families (it starts with a young Celtic boy on the eve of the Roman invasion, and passes through the generations to end with one of his distant descendants in the 21st century). Bloody good read, and was my favourite book for a very long time.
It was recommended to me by my dad, who said that he had one minor gripe about the book. It contained (by necessity) a family tree so you could keep track of who was descended from who (family names evolve or change through the story, and the book naturally skips several generations at a time). The only trouble was that whenever you turned to the family tree to see who you were now reading about, you'd also find out who they were later going to marry and have kids with. Since some parts of the story revolve around the question of whether a particular relationship's going to work out or whether a character's even going to live long enough to marry, the damn family tree was a constant source of spoilers.