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....
Ahem!

I would like to elaborate on a few of your points, in my own perspective.
I believe he is with Dumbledore...Erm...'was'... sweatdrop
My theorey is that Dumbles in the end, ordered him to kill him, instead of sacrifice himself, Snape being a very important attribute to the War.
I think Dumbledore believed that it was Harry's time to be alone, and that he no longer needed him, and old man, who was dying anyway (remember the hand?).
Snape says at the beginning of the book, that he knew of what the Dark Lord wanted Draco to do, so, Dumbledore must have to, by way of Snape. I believe they either already went through the possibility that Narcissa might come to him, or Snape knew he couldn't defend himself against two powerful witches, alone in his cottage, so he made the Unbreakable Vow in order to gain himself time, and Guidance to Draco.
Also, killing Dumbledore ensured Snapes 'fidelity' to Voldemort, in the eyes of most people, which I believe was the goal from the very beginning, so he could continue his spy work.

As for Snape being mean to Harry...Have you ever considered that he had to be? He was trying to preserve a very delicate sense of trust among him and other Death Eaters, and members of the Dark Side, in case of the imminent uprising of Lord Voldemort himself. Dumbeldore knew that he would come again, as he knew of the Horcruxes. Who's to say he did not warn Snape of the same?
Also, I don't think it as anythign at all to do with Harry's parents, maybe at first, but not anymore. He could, quite possibly, genuinely dislike the boy. He may be the 'Savior of the Wizarding World', but no one, by any means, has to like him, now do they?
Snape may respect the role Harry has to play in the War, but he still may dislike his personality, and actions.
And whyb on earth should he like him 'because it was Dumbeldore's wishes'? I don't think it ever was. I think Dumbeldore respects the fact that you can't love everyone, and gave up on trying to kindle a friendship between the two. Dumbeldore knows you can't force someone how to feel, and Snape is not one to take idle orders. He would never obey such an order as 'to be nice to The Boy Who Lived'. And order to kill him, to sacrifice Dumbeldore in order to stay the Side of the Light in it's role, but not how he should act.
Honestly, would you?

Awwwws! I didn't mean to make you feel bad! *huggles*

I believe Snape is acting for Le Dumblie. I was with that before, but Vanir brought up some good points.

I also maintain the way to not get upset about HP deaths is to make up theories about how they could still be alive. Dumbledore may liiiive. And sadly so may Sirius, due to what ever Luna said. But Dumbledore may be dead. Shwatever. Maybe if we knew more about his defeat of grindlewald? Maybe that will come up in the next book.

Damnit I want that book so bad. sad

Well, I'd have to say that Snapie should come with a sticker on his forehead saying "Do not judge untill seventh book"

Yeah, I'm pretty befuddled myself.

So do I!