Theory

Harry got value number 711 at Gringotts. Hagrid took the package containing the Philosopher's stone out of 713. So what's in 712?
Rowling is obviously drawing our attention to it (otherwise the numbers of the other two values would have been further apart, no?). I'm willing to bet that it's coming up later in the books.

What is this never-ending talk about watches? Call me paranoid but there's something very important about watches. Maybe there's a bigg-ass time turner in 712, which Harry will use in the 7th book and finish Voldie off before he gets too powerful. (If he does it when Voldie is just a kid, then I'll scream murder and hate Harry for all eternity.)

In an interview, when asked where she'd go if she could travel to Hogwarts for an hour, Rowling replies: "Go straight into a certain room, mentioned in book four, which has certain magical properties Harry hasn't discovered yet!"
Not this mystery room must be one he's been in. At first I thought 'It has to be that room Dumbledore told Karakoff about', but if Harry hasn't discovered whatever yet, then he must have been in it, right? So there goes that room.
We have the broom closet, where Rita Skeeter interviewed him. Though I can't really see a *broom closet* being called a room. In my mind it's far too small.
We have the prefects bathroom, but I doubt it.
Then we have that room where they gathered up the champions in behind the Great Hall. That's a room. He's been in it, but never for a really long time. See?

According to Rowling Trevor, Neville's toad, is still lurking around, even though he's not really been mentioned for a long time. Now, being the paranoid person I am, I'm starting to get more and more convinced that since MWPP became animagus (okay, so only WPP) and they were just students there is a possibility that there are more lurking around. Trevor might be one of them.
I'm not saying at he's evil, but wouldn't it make sense? He'd have reason to run away all the time (try to find out things that he wouldn't be able to if Neville kept him in his pocket or wherever), and he'd survive even though there's cats running around all over Hogwarts (if cats eats bugs I wouldn't rule out the possibility of a nice toad).
All in all. Trevor is really an animagus and a spy. If no then he's in the mystery room or in Trelawney's office, high beyond belief.

Doesn't Crookshanks seem a little too smart? Does average cats recognizes animagus in their animal shape? No. Does average cats take pieces of paper from a table and gives it to people they like? No. Does average cats run to lay ontop of people's chests when someone is threatening to kill the person? No.
Crookshanks is a good guy, hopefully. He might be a former Death Eater hiding from Voldie or something. Or maybe he's hiding from someone or something else, but that cat just can't be a cat!
Then Mrs. Norris. Couldn't she be a human (possibly a witch or a squib) who is trapped in a cat body because of some spell? Or maybe I'm just being paranoid. In this case I don't have as much to come with, but what is up with her looking through the invisible cloak? *shivers* One of these days (books?) we'll find out.

Honestly, I'm not just saying this because I think they belong together (they are the couple). Dumbledore said "Stay low at Lupin's" didn't he? *grins* Now in my eyes that can be twisted into something, eh, interesting. Besides, wouldn't it just be great if they turned out to be a couple? Rowling would teach kids about homosexuality at the same time she makes all the Remus/Sirius shippers happy!

You know what I hate? Snape *always* being the bad guy. He saved Harry's life, he risked his life to keep the philosopher's stone safe, he went to face a mass murderer and a werewolf (who hadn't taken his potion, and it was full moon) to save the three students he hates the most on his own. Still he's somehow the bad guy.
Okay, Snape might not be the nicest of people, but he had no reason to save Harry's life, he could have just ignored this and let Quirell finish him off (and does he get as much as a 'thanks'?)
Besides, remember that the Potters were warned that Voldie was after them? Yeah, which Death Eater could possibly have had it in his interest to go against Voldemort and save innocent people at the risk at his own life? Snape.
So, not only does he attempt to save the Potters, but when his efforts turns out to be in vain and James and Lily are killed anyway he takes on the role as a protector (kinda) for their child when he comes to Hogwarts. And the thanks Snape gets? Oh, he's just their main suspect of everything and anything bad that happens at Hogwarts. Nice. I don't blame him for having a grudge at the trio.

Remember when Harry heard his mother scream in book 3? And how he heard Voldemort say that she didn't have to die? Yeah, that made pretty much everyone go 'Huh?'. Why would Lily be spared when James and Harry (who was just a baby) had to die? Well, she was married to James, so she wasn't really a Potter. Whatever Voldemort feared must have had something to do with the Potter clan, why would he else go after the baby?
Everyone assumes that Snape was in love with Lily, and that's why he hates Harry so much. But what if it wasn't Snape who loved Lily, but Peter? Wouldn't that be enough reason to start hating James, and if then Voldemort offered to kill James and Harry (being the only Potter by-blood) and leave Lily to Peter as a reward?
Peter was the weak one of the group. The only other possible weakness would be Remus, being a dark creature (Voldemort states in book 4 that the dementors will join them since 'they are our natural allies'. That is most likely to go for most dark creatures, if not all), but it's possible that they (thanks to someone who had gone to Hogwarts at the same time) knew that Peter was more likely to break. And then *scary music* They were right.
Peter becomes a DE, tells Voldie that he is the secret keeper and is promised Lily as a reward. Lily won't let Voldemort kill Harry so she is killed too, even though she wouldn't have to die.