At once both healer and killer, prodigal son and parricide, Christ figure and devil's disciple, chess master and pawn, spider and fly in the web, Harry's mirror and his shadow, Snape is by far the most complex and fascinating character in the books.

Ah, beautifully said! And I think JKR does have an idea about what she did there. I can't wait - well, obviously for DH, but also for her post DH interviews.

Hermione remarks about Snape's old textbook that the half-blood prince seems to her to have a nasty sense of humor.

Does she? Do you happen to have the chapter number/context or something. I can't remember and would like to read it.

I don't know exactly how much older Malfoy is than Snape and Black, but this quote made me think they were all at school together, with Lucius Malfoy in his sixth or seventh year when the other two were eleven.

You probably know now that interviews etc. pretty much prove you right.

Many of us fans have been asking just what happens here, what Snape's loyalties and motives truly are, and, in particular, what that twitch means.

For me it seemed quite clear that he knew what he did and that was promising something that would make him twitch. I don't think he would twitch for uncertainty. Uncertainty is his daily business.

PS: Your html is messed up. You need to delete at least one tag after the point it breaks.