Okay, so, I said I'd write more on Dumbledore once I'd given myself some time to digest DH, so here it is:
Re: The Ariana business.
I've read some good discussions of this part of the Dumbledore backstory, particularly this one, where the author rants about discusses whether or not Albus' resentment of Ariana was believable. She concludes that it is, citing her own experiences with a handicapped sibling as an example. I agree with her conclusion. I don't think it remarkably earth-shattering to find that a brilliant teenaged Albus, having a handicapped sister, would have resented her at least a little for holding him back. I don't think this makes any real dent in his character as we knew it pre-DH. I agree with Hermione, that Harry was only really angry because Dumbledore didn't tell Harry himself. IMO, Harry is very quick to take offense when people hold out on him because he has serious abandonment issues (probably has something to do with growing up in a cupboard). This is especially true of his relationship with Dumbledore, because Dumbledore keeps a multitude of secrets and Harry tends to assume that this means that Dumbledore doesn't care about him. (More on that assumption later).
Re: The Grindelwald business
This bothered me when I first read the book, but now that I've thought about it, it makes a lot more sense. At first glance, one is tempted to say something like: O_o Dumbledore was a wizard-supremacist? What alternate HP universe have we just entered?
However, we must look at Dumbledore's note to Grindelwald in the context of what happened to Ariana. Remember that by the time he meets Grindelwald, muggles have essentially ruined Albus' family life, and destroyed his sister's health permanently. Yes, it was only a select few, but I think that makes his, er, bias towards muggles a bit more understandable, yes? He's seen the damage muggles can do first hand, and he's very keen not to see it happen again. If this means that wizards will have to control muggle society, well, he thinks, then there won't be any more Arianas.
I don't think Albus' mistake here is catastrophic to his character either. I see it like this: Albus felt helpless, lonely, and unrecognized. He saw what happened to his sister and thought, in a somewhat typical teenage fashion that, "If I were in charge, things like this wouldn't happen." Along came Grindelwald who was brilliant and acknowledged Albus' brilliance as well. Albus took to him immediately, and they started forming plots to seize power and mold the world into their own image. If Albus had a few reservations about Grindelwald, he shoved them aside, because he saw Grindelwald as his only chance to make something of himself. He thought himself invincible, that even if he made a "deal with the devil," so to speak, he could still make it work out in his favor. Then, when Ariana died, Albus saw his mistake, realized what "taking control" would really involve, and did a personality 180. He then avoided too much power for the rest of his life, because he didn't trust himself not to let it go to his head and make him return to a place where he thought all the world's problems were just a ministry ordinance away from being fixed.
After thinking about all this, I don't find this very earth-shattering anymore. So, 17-year-old Dumbledore thought he could save the world by controlling it, realized he was wrong, and changed his mind. ... okay? This makes a difference in our idea of Dumbledore-as-we-know-him-now why?
Re: The Dumbledore & Harry relationship
I think that, of all the new Dumbledore information in this book, it was the bit about him, essentially, leading Harry to get killed that had the greatest potential to ruin my image of him forever. Yes, had. I liked Dumbledore's character pre-DH and I still do now.
I think that saying that Dumbledore essentially raised Harry to die is oversimplifying a great deal. I think that Ariana's death affected more of Dumbledore's personality than just the wizard-supremacist bit. I think he also realized, after she died, that power would involve being responsible for other people. For Grindelwald, this didn't matter, because he didn't care about what happened to other people anyway. But for Albus, who had a clear sense of right and wrong, taking power and being responsible for the deaths of countless people in the process, was repulsive.
In this context, I think that Dumbledore would've hated the idea of being responsible for Harry from the beginning. He says to Harry in OotP, "I never thought I would have such a person on my hands." Think about how Dumbledore has carried around the ghost of his dead sister for over a hundred years, ie, he still sees her in the mirror of erised, still loses his head in HBP when he thinks he will see her again, etc. This is not a man who could ruthlessly send Harry to his death knowing that he is responsible without hating himself for the rest of eternity. And yet, pre-GoF at least, he knows that it is a possibility.
But, he also knows that if Harry is indeed a horcrux, if he, Dumbledore, does nothing, Voldemort will never be defeated and more and more people will die.
This only gets more and more complicated as Dumbledore grows to love Harry, and conversely, Harry grows to love and trust him. Honestly, I think Dumbledore was doing a ridiculous amount of compartmentalizing in books 1-6. He knew about the prophecy, but worked very hard to convince himself that he wouldn't have to worry about it for a long time. He began to suspect horcruxes, and that Harry himself was one, but tried to convince himself that he was wrong. (In HBP, he says that he might be wrong about the horcruxes, whereas I now think it should have been prefectly obvious even before Harry got Slughorn's memory, don't you?)
In my view, Dumbledore didn't want to lead Harry to his death. He didn't want to let Harry confront Voldemort at all. But he didn't think he had any better option, and he also realized that Harry would only let Voldemort take over over Harry's dead body, literally. So he did the best he could to ensure that Harry was best prepared to defeat Voldemort and (hopefully) live. He was torn between trying to save Harry and trying to save the world, and it wasn't his fault that they were mutually exclusive. He wanted to be able to put Harry first, felt responsible for Harry's life, but at the same time, as the "greatest wizard of the age" and mentor of "the chosen one" he felt responsible for the rest of the world too. (Speaking of which, if you want to make a case for self-sacrifice, I dunno why anyone bothers with Harry. You'd have a much better case with what Dumbledore does to himself by "sending Harry to his death." It's kind of like killing your own kid to save the rest of the world, isn't it? Well, I don't think so, really, but you could certainly argue it.) I don't think he kept other people from the truth because he was afraid they would try to save Harry. I think that he kept them away because he wanted Harry to have at least *one* adult figure who didn't have to choose between Harry's life and the life of themselves/their children/the entire world. What do you think Molly would have done, given the information that: Harry has to die, or Voldemort will kill your whole family. Add in the fact that Harry would've been falling over himself to jump in front of any AK headed for the Weasleys, and, well, you can imagine how well it would have worked out for *everyone* to know that it was Harry-or-them. Dumbledore, effectively, took the blame upon himself, and hated himself greatly for it, I might add, if the tears and self-loathing at the end of DH are any indication.
I'm not convinced that, if the blood-bond thing which saved Harry hadn't happened in GoF, that Dumbledore wouldn't have broken down and sabotaged his plan before the end anyway. That's the original reason I thought he would die in HBP (before it came out) because I couldn't see him actually, when it came down to it, letting Harry face Voldemort alone unless he was already out of the picture. For all that the plan worked in the end, Dumbledore really wasn't very good at the whole not-caring-about-what-happens-to-Harry thing.
And one more thing...
The only thing that really still annoys me about Dumbledore is how misguided his self-hatred really was. He got all worried about Harry knowing about Ariana, when that really wasn't what made Harry angry with him. Dumbledore never seemed to get that all Harry wanted was some evidence that he hadn't been imagining things when he thought Dumbledore cared. This is what made me the most angry both in OotP and DH. It's so stupid, because poor little love-starved-until-he-was-eleven Harry doesn't get worked up about being lied to, manipulated, or whatever you want to argue that Dumbledore did to him. He gets angry because he thinks Dumbledore didn't love him. He's used to everything he loves going up in smoke. So the first conclusion he jumps to whenever Dumbledore does something he doesn't like is, "the only bit of me Dumbledore cares about is my scar." I would've felt better if Dumbledore had apologized for *that*, instead of the Ariana business, or the Grindelwald business, or even the manipulation/sacrifice business. Because *that* would've been so easy to fix, if Dumbledore had taken a moment a way from feeling guilty about every mistake he's ever made long enough to give Harry a freaking hug. Seriously, it was his guilt that annoyed me more than anything else. Self-loathing is never flattering, but it was particularly unflattering on Dumbledore. Yuck.
... I think I'm done for now. I'm sure I've left things out, but it'll have to do for now. Love to hear your thoughts!