The first page isn't intersting, but there are some things I wanted to respond to starting from page 2
The xover of major muggle and wizard events/wars - OMG, don't even try to put those together. Especially not by someone with only a layman's (or less) understanding of history and politics. I can buy something like that out of, say, Harry Turtledove or Eric Flint, who actually do comprehensive research on the moments in history they open their mouths about. But JKR? Stick to imaginary wand-waving. Please.
Muggle to Wizard population ratio - Well, at least JKR honestly admits that she's hopeless at math. How else do you come up with 40 kids in one grade level (Harry's) and then blurts out 600 for the student population of Hogwarts... yeah. But ~3000 wizards in Britain? With only a tiny portion of even those (see page 3) working for Voldemort. And yet they can be a global threat to the world? And with the pitiful magicks that the Potterverse has shown? Excuse me for being skeptical, to say the least.
The anti-shipping stuff - Okay, this time it's the interviewers being an idiot, and JKR is at least smart enough to be politic to avoid breaking her food bowl. But it brings to mind the fact that these people are utter idiots for not realizing that for any story, once it's published and read, becomes the interpretation of the reader, whatever the reader believes. The writer has no right to the readership's (or a reader's) beliefs on how things should be in the story.
Draco - I'm not touching this one with a 10-foot pole. I'm sure cashew
will have something to say about it though. :p
The prophecy - I think this is probably the only worthwhile information given in the interview (it's on page 3). Basically, the prophecy regarding Harry and Voldemort was more of a MacBeth/Oedipus kind of self-perpetuating prophecy than a Tolkein or standard sci-fi/fantasy "it *must* happen this way and the timeline is set" kind of prophecy. That bodes well for fanfics, if nothing else. :p
The rationale for Slytherin House - Regardless there were some actually decent sentiments in Rowling's reply, the sheer condescension of the reply and the tone of the interviewer just... argh! Irritates me, to say the least.
Snape - I know there's oodles of ambiguous clues in the books pointing that Snape's allegiance is still with the side of light. But from a lot of Rowling's responses (as well as her personal dislike of the person she based the character on), it seems that one of the twists in the next book might be that Snape is actually evil. While at this point, I'm not sure I'd care that much about the good side winning, I do think that would be such a cheapening/slaughtering of his character after all this time. It'd be pointless. Meh.