Well, I've been a'thinkin and I think I have a pretty sweetbees theory regarding Harry and the Horcruxes. There are, as I see it, two possibilities that will basically decide the end of the book: 1) Harry is Horcrux or 2) Harry is not a Horcrux. I think these are both probable--there is evidence for both.
In regards to #2, I am inclined to believe he is not a Horcrux because I think Voldemort would have made his 7 Horcruxes by this point in his career. He would have made them early, before a serious bid for power or the war, as security. Also, Voldemort went to Godric's Hollow to kill Harry, not to make him a Horcrux. Thus, if Harry IS a Horcrux...
...It was an accident. I don't know the method for creating Horcruxes, but possibly it could have been an accident when Voldemort killed Lily (since he wasn't originally planning on killing her) or perhaps when his killing curse rebounded off Harry. So the way I see it: either there are 7 Horcruxes, and Harry is a non-Horcrux or there are 8 and Harry is an accidental one.
So, if Harry IS a horcrux, here's what I think will happen: Harry will have to overcome his fear of dementors (And Lupin will have to stock up on chocolate). A dementor is the only thing, I think, that could extract the portion of Voldemort's soul from Harry without killing Harry in the process. Since the dementors are breeding now they must be in pretty ready supply, too. So, here are some remaining questions:
1) If he is a Horcrux, how will Harry figure this out? Dumbledore told him that Voldemort transferred some of his power to Harry, will this clue Harry in? Maybe the question is: how long will it take Hermione to figure it out?
2) Is Voldemort aware that Harry is a Horcrux? He knows they have a connection, and you would think someone would notice losing a bit of their soul. Still, you may not notice if it happened while you were being ripped from your body.
3) How will Ginny and Tonks die?
And of course there are all those other pesky questions: How will he find them? How will he destroy them? He destroyed the diary, yes, but if it's that simple then why did Dumbledore get a blackened hand? I mean, really, how will he find them? I'm very concerned for young Mr. Potter. Early word is that there's a target release date for July 7, 2007...7/7/07. Hahahah, look at all those magic numbers.
P.S.: Cho is still an evil Ministry infiltrator.
P.P.S.: How will Ginny and Tonks die?