Assuming the author isn’t in the habit of deliberately misleading readers by posting false information on her website, Crookshanks isn’t an animagus.
A quick bit of reasoning:
Fact: Harry had the opportunity to be in Slytherin
Assume: this means Harry is a pureblood
It follows: this means Harry’s parents were both purebloods
Ergo: Harry’s aunt Petunia is a pureblood squib
Therefore: Dudley Dursley has half wizard’s blood.
But this doesn’t really follow. It’s seemed pretty clear to me that Lily Potter was a freak witch coming from a normal family–like Hermione. That would make Harry not pureblood and therefore… not a candidate for Slytherin in the first place. Right?
Voldemort wasn’t pure blood either. I don’t think that’s a true qualification to be in Slytherin.
It’s a problematic inconsistency, then. The Sorting Hat’s song at the beginning of OOTP talks about Slytherin being a place that caters to purebloods (the nasty variety); also, when Malfoy is taunting Harry and his friends, he only levels “mudblood” at Hermione, not at Harry… right?
Yep. One of the deleted plot lines JKR describes on her web site involves the daughter of a Squib and a Muggle being sorted into Slytherin (the character was dropped for reasons unrelated to her bloodline or House placement). I think the Hat will put any student into Slytherin if they show enough cunning or ambition and they want to be there, regardless of their background; it’s just that most Muggle-born students don’t want to.
(Sorry for the double-post – Sattua got in there after I started composing the last one.) The Sorting Hat’s song in OotP says that Salazar Slytherin wanted to teach only pureblooded students a thousand years ago; it doesn’t follow that the Hat necessarily honors Salazar’s wishes now.
“Mudblood,” as far as I can tell, is an insult leveled only at Muggle-born witches and wizards, not half-bloods, and in any case, Draco Malfoy doesn’t necessarily know that Harry is a half-blood. The only thing Harry’s told him about his ancestry is that his parents were both magical, and the none-too-savvy eleven-year-old Draco apparently assumed that this meant he was a pureblood.
Thanks for the clarification. I have just bought Harry’s school books, both for me and for my ten-year-old cousin. I bought the pack of two–the one about magical creatures and the one about quidditch. Are those the only two?
The Hat doesn’t follow the four Founder’s wishes to the letter. In that same song, it says that Godric Gryffindor chose students who had “great deeds to their name” or somesuch. I strongly doubt that Gryffindor House is populated with 11-year-old children who have accomplished great deeds.
The Hat sorts based on personality. Brave people go into Gryffindor, cunning & ambitious people go into Slytherin, highly intelligent people go into Ravenclaw, and everyone else goes into Hufflepuff. (and yes, I think it’s become pretty clear that Hufflepuff is the “miscellaneous” category.)
As for the Half-Blood prince: I say Goderic Gryffindor, or a descendant of his. Altho’ given how Rowling likes to mislead people, it’s probably going to be someone completely out of left field, like Filch.
My thoughts…
Godric Gryffindor–It’s predictable, but it could work… if JK writes it really convincingly, involving all sorts of cool tricks with time travel and apparations and the suchlike.
Aberforth–I think he’s more of a running joke than an actual character (inappropriate charms on a goat, sounds like an SDMB member in disguise ;)); then I remember Mrs. Figgs, who actually got developed from one-dimensional caricature to three-dimensional character. It’s possible, but again, JK would have to do it really well.
Lupin–He has shabby clothes and that battered old briefcase all the time… I dunno, but I think a prince would look more, well, royal. He could always be in disguise, but I have my misgivings. Still, I think he’s the strongest candidate so far.
Neville–If the paragraph on the website is right, then Neville is way too young. But if it’s not, it’s a fascinating angle on the story.
Hagrid–The only way I can see him elevated to princely status is through the giant society we saw in Book 5, and he’s most definitely not a part of that. Plus, he doesn’t fit the description on the website.
Could the Prince be Dumbledore himself? Or even… Nearly Headless Nick?
I think it’d be the coolest if she did make up a new character. 
Has it been ruled out that the half-blood prince could be Voldemort?