What is Snape's true allegiance?
The true allegiance of Professor Snape has been one of the great mysteries of the whole series: is he evil or just greasy? At this point, the volume of evidence stacked against him is overwhelming. He was formerly an evil Death Eater. He was the head of the evil Slytherin household. He has evil black hair. He is played by actor Alan Rickman, who is himself evil. This is some pretty damning stuff.
On the other hand, Dumbledore trusted him, and Dumbledore seemed to know most things about most things. Dumbledore was pretty old though, and old people do crazy things all the time. I once had an elderly relative who stood up and started applauding at the television. He was watching The Muppet Show. That was pretty weird.
Temporarily setting aside the possibility that Dumbledore was senile, one unavoidable fact remains: Dumbledore was murdered by Snape. That pretty much proves Snape is evil, right?
In the opening passages of The Half Blood Prince, Snape agrees to an Unbreakable Vow to "aid Draco on his mission, and complete it should he fail." A careful reading of this chapter reveals that Snape may have been fishing for information during this whole passage, possibly acting in his role as a spy for Dumbledore. As such, he may not have fully known what Draco's mission was when he was trapped into making the Unbreakable Vow. Thus when he smote Dumbledore off the balcony that fateful evening, he may have literally had no choice.
Or, and we're not discounting this, maybe he's just a huge evil dick.
Our "100% Lock, Money-in-the-Bank" Prediction: Occam's Razor suggests that the simplest explanation-Snape is evil-is likely the correct one. But for Snape to be truly evil, that means that Dumbledore would have been wrong about something. And until we see proof of that, we're going to stick with our needlessly convoluted conspiracy theory. In other words, f**k you, Occam's razor. You're one smug principle we can live without.
Is Harry a Horcrux?
If you haven't read The Half Blood Prince yet, then first, we're super sorry about those flagrant spoilers above, and second, you probably don't know about Horcruxes yet. Horcruxes are magical artifacts that supposedly contain fractions of Voldemort's soul. It's expected that the main narrative of The Deathly Hallows will be about Harry's hunt for the remaining Horcruxes before his final confrontation with Voldemort. If this is true, it means that the final Harry Potter Book will have the same plot as basically every RPG ever made, what with Harry having to "collect the Seven Important Things" to defeat the "loosely explained magic barrier" which will allow him to access the "final dungeon," and in the end he'll still be a "massive nerd."
The identity of all the Horcruxes isn't entirely known yet. Most are suspected to be mundane personal objects (lockets, diaries, body-grooming razors, etc.). However, one of the most popular theories floating around the Internet right now is that Harry himself is a Horcrux.
This fits somewhat with what's known about how Horcruxes are made. A Horcrux has to be made after a murder, it can be a living creature, and it's usually something that's meaningful to its creator in some way. All of these rules could be said to apply to Harry (or his scar). Further supporting this, Harry's scar does have a weird spooky connection with Voldemort, and Harry himself has said that Voldemort put a "piece of him inside me," before quickly adding "but not in a gay way."
But-and much like the one on Aunt Marge, this is a big but-since he was resurrected, Voldemort himself has tried to kill Harry at least twice. He wouldn't do that if Harry contained an important and irretrievable part of his soul. That's a little bit like banging your penis on a hot stovetop to get rid of crabs.
The only way this theory works is if Voldemort didn't know he'd made Harry his Horcrux... which would imply that Voldemort is pretty casual with pieces of his soul. The guy probably listens to Fall Out Boy by the ton.
Our "100% Lock, Money-in-the-Bank" Prediction: Harry's not a Horcrux. For Voldemort to have accidentally created a Horcrux after what was, for him, just a routine double-murder, implies that murderers could have been accidentally making Horcruxes (and thus becoming immortal) for centuries. That's absurd- not Quidditch-level absurd, but still pretty out there.
R.A.B. was the author of the mysterious note in the locket/potential Horcrux that Harry and Dumbledore retrieved just prior to Dumbledore's death. The note, addressed to Voldemort, claimed that the author had stolen the original locket, which he knew to be a Horcrux, and would destroy it. The author didn't sign his name, instead choosing to sign the note with the initials R.A.B. because... well, because J.K. Rowling knows that screwing your readers out of vital information is a good way to sell books, we guess.
According to the Internet, the leading candidate for the true identity of R.A.B. is Regulus Black, brother of Sirius Black and former resident of The Order of the Phoenix's headquarters, 12 Grimmauld Place. He was a former ally of Voldemort, and large heavy lockets have been seen in his possession. In fact, Regulus Black is such an obvious choice to be R.A.B., that many fans theorize that he must therefore not be R.A.B. due to Rowling's well-known espousal of the Opposite-Land school of mystery plotting.
But let's step outside the confines of the Potterverse and into the real world for a second. Harry Potter is printed in dozens of different languages, many of which sometimes have slightly different names for the main characters, as dictated by whatever linguistic peculiarities that particular language has. For example, in Germany, "Harry Potter" is translated as "Brody Hasslehoff." All of the foreign editions of the books that have different names for Regulus Black would also have different corresponding initials in place of R.A.B.
Our "100% Lock, Money-in-the-Bank" Prediction: This one barely qualifies as a prediction. It's Regulus Black. End of story. This mystery will probably be "solved" in the first act of the book, shortly before Neville is sexually assaulted by a half snake/half hamster.
Now that's a prediction!