http://www.madamscoop.org/themes/book7.htm

• JK says about Sirius Black: "I do like him, although I do not think he is wholly wonderful." She says he is "brave, loyal, reckless, embittered and slightly unbalanced by his long stay in Azkaban," but his redeeming quality is the affection that he is capable of feeling. He loved James like a brother, and has attached that affection to Harry.

• JKR: "What's very important for me is when Dumbledore says that you have to choose between what is right and what is easy. This is the setup for the next three books. All of them are going to have to choose, because what is easy is often not right." [Read the exact quote from Entertainment Weekly, 2000]

• JKR: "Key things happen in book two. No one knows how important those things are ... yet. There's a lot in there. And I know how difficult it was to get it all in there without drawing too much attention to the clues." "All the important stuff [from book 2] got into the film."[IGN-02]

• Kloves: "There's one thing in Chamber [of Secrets movie] that Jo indicated will play a part later in the series..." [CoS-03]
• JKR: "In book six, the wizarding world is really at war again and [Harry] has to master his own feelings to make himself useful." [Read the exact quote from World Book Day, 2004]

• Harry Potter and the Half-Blood Prince "was once, in the long distant past, a possibility for 'Chamber of Secrets,' and from that deduced that it was genuine. Certain crucial pieces of information in book six were originally planned for 'Chamber of Secrets,' but very early on (first draft of Chamber) I realised that this information's proper home was book six. I have said before now that 'Chamber' holds some very important clues to the ultimate end of the series. Not as many as six, obviously, but there is a link." [Read the exact quote from Jo's website]
• There is no trace of the HBP storyline left in CoS, rather the link between the two books relates to a discovery Harry made in CoS that foreshadows something he finds out in HBP. [Read the exact quote from Jo's website]  

• JKR came close to using a chapter very like the opening one of book 6 in PS/SS, PoA and OotP. But it didn't fit properly until now. [Read the exact quote from Jo's website]

• None of the pure-blood families are actually ‘pure’ – they merely cross Muggles and Squibs off the family tree. The number of families who can claim to be pure is diminishing as they are finding it increasingly difficult to perpetuate themselves. This subject is touched upon in book 6. [Read the exact quote from Jo's website]

• JKR on the last chapter of book 7: "this is really where I wrap everything up, it’s the epilogue. And I, I basically say what happens to everyone after they leave school – those who survive – because there are deaths – more deaths coming." [Read the exact quote from "Harry Potter and Me," 2001]

What about Snape?
JKR: Snape is a very sadistic teacher, loosely based on a teacher I myself had, I have to say. I think children are very aware and we are kidding ourselves if we don’t think that they are, that teachers do sometimes abuse their power and this particular teacher does abuse his power. He’s not a particularly pleasant person at all. However, everyone should keep their eye on Snape, I’ll just say that because there is more to him than meets the eye and you will find out part of what I am talking about if you read Book 4. No, I’m not trying to drum up more sales, go to the library and get it out. I’d rather people read it.

One of our internet correspondents wondered if Snape is going to fall in love.
JKR: (JKR laughs) Who on earth would want Snape in love with them? That’s a very horrible idea.

There’s an important kind of redemptive pattern to Snape
JKR: He, um, there’s so much I wish I could say to you, and I can’t because it would ruin. I promise you, whoever asked that question, can I just say to you that I’m slightly stunned that you’ve said that and you’ll find out why I’m so stunned if you read Book 7. That’s all I’m going to say.