Just finished reading HBP, well behind the rest of the civilized world, and, yep, it turns out I was spoiled. Damn you, guy on a random Fark thread!
So, several days before I got my hands on HBP, I saw a comment in a Fark thread (totally! unrelated! dammit! I was being careful!) which read SNAPE KILLS DUMBLEDORE. I think there may have been a HA HA! in there somewhere, too. Given that it was a random unrelated Fark thread, I thought there was a chance it was a fake spoiler and somebody was just being a jerk, but, well, not implausible; people had been saying Dumbledore might be next to die, and Snape is... Snape.
Maybe it's just because I'm contrary, but I immediately started trying to work out how, if true, that bald statement--Snape kills Dumbledore--might be misleading. So when I got to Chapter Two, and Snape made the Unbreakable Vow, I had it pretty much sussed: Draco was supposed to kill Dumbledore, and Snape, angling for information, had just committed himself, sight unseen, to doing for Draco whatever it was Draco was supposed to do for Voldemort. Again, maybe it's just my contrariness, or my determination to see long-running characters as sympathetic, or maybe it really is right there in the text of Chapter Two, but it seemed very clear to me that Snape was going to do this thing to protect Draco, not just from the consequences of failure, but from the consequences of success.
It was strange, reading the book and knowing that for once, Harry's obsession with Draco was completely correct; knowing how it would play out; knowing that Dumbledore would die, that he had to know it as well and be preparing for it. So that's my reading: Snape is a triple agent, trying desperately to protect just one foolish and endangered student, who might just have finally learned a lesson this year, and, really, trying just as hard to protect Harry--also endangered, perhaps also foolish, definitely not fully informed. I think Dumbledore was fully informed, I think that was what he and Snape argued about, and I think Dumbledore had a very specific reason for sending Harry to fetch Snape--he knew that he was dying, and he knew that if he died before Snape could kill him in Draco's stead, Draco would be punished, and Snape might die as well for failing in the Vow. I think Immobilizing Harry at the last was partly a matter of expedience; he had to react on a split second, and he was perhaps too weak for very complex spellwork. Then too, he may have hoped that Harry, seeing exactly what transpired, would eventually be able to understand the truth. Surely, if Harry hadn't seen, it would have been worse. I think Snape took Draco and headed off to the Death Eaters--to continue carrying out Dumbledore's orders, just as Harry is.
And I think it was Regulus, and I hope he succeeded before he died, poor pup, and saved Harry a little work.
Oh, and I guess I was spoiled for the Lupin/Tonks thing, in that I glimpsed a mention of the existence of a Lupin/Tonks thing, and... I dunno, I think it works. Having read the whole thing watching Lupin and Tonks for signs of a Thing, yeah, I think it's there, and done pretty well, given that it's so very very peripheral to Harry's interests.
So, yeah. I haven't read much spoilered discussion, for obvious reasons, so possibly I am just stating the excessively obvious, but it makes me happy to have opinions. *g*