I just finished rereading all six of the Harry Potter books today. I had started this project, oh, a month or so ago, and it was well worth my time -- as Christine suggested might happen, I became completely immersed in that world. And I caught stuff I missed the first time 'round, since I wasn't in such a hurry to find out what happened. And I'm even more excited for the last book to publish. Well, or the next book, anyway.
See, I have a few cockamamie theories concerning the Potter series. I actually think there will be 4 more books. Why, you ask? Well, for starters, Harry has to find 4 horcruxes and then kill Voldemort -- a big task for just one more novel, if you ask me. (See, find one horcrux per novel, then also kill Voldemort at the end of the last one.) Also, Harry technically has one year left at Hogwarts, then will be required to do some sort of wizard college, since he wants to be an Auror. (I'm sorry if someone who hasn't read the books is reading this -- you have no idea what I'm rambling about.) Also, I think ten is a nice number of books -- much more well-rounded than seven.
Other conspiracy-type theories: I think Sirius Black will come back, and I'm not entirely sure Dumbledore is dead. I still think Snape is working for the "good guys" -- although there is the problem of that unbreakable vow thing he formed at the beginning of book six. Perhaps he "had" to kill Dumbledore, because of the vow, and didn't know what he was agreeing to at the time. Or it could be a big, fat setup -- Snape was in on faking Dumbledore's death or something. Who knows. But it's incredibly interesting fiction!