While I'm only starting my rereads, this was a super fun one - JKR, either purposefully or by going back and then figuring out how to tie all those loose ends, really did something here. Besides the very obvious  Horcrux clues , that will come back to us in Hallows, there are some marvelous lines that hint on the future of some characters (I distinctively remember some Percy foreshadowing), and she just knows how to sprinkle in what seem like throwaway lines with things that will come back to us further along, even if not in the way we expected (i.e. Vanishing Cabinet). All those Easter Eggs just make the reread super enjoyable. And also, it's always great to come back to Hogwarts.