(The HPMOR discussion thread after this one is here.)
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. There haven't been any chapters recently, but it looks like there are a bunch in the pipeline and the old thread is nearing 700 comments. The latest chapter as of 7th March 2012 is Ch. 77.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight, nine.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
I see also that the theories about Santa Claus's identity are equally as varied as the ones about Mr. Hat & Cloak. My take on this is similar to my take on H&C: we're meant to understand that Santa Claus is simply Dumbledore.
The only person we know for whom all the above facts are true is Dumbledore.
However, the "S" who left notes for Hermione is not Santa Claus. It's Severus Snape, who we know for a fact was the mysterious person helping SPHEW in its mission. The two signatures happen to both begin with S, but that's a coincidence; if the writer had intended Harry and Hermione to figure out that the two note senders were the same, they would have signed the letters to Hermione "Santa Claus" or at least "SC". Therefore, "S" doesn't know about the first notes and was not trying to connect his notes to them.
Let me add to my previous hypotheses about Eliezer's state of mind while writing: The fact that something is entirely mysterious to the characters does not mean that it's supposed to be entirely mysterious to us. We are certainly meant to know that "S" is Snape. We know this because of Interlude with the Confessor. It could not be any more blatant without being stated in the Author's Notes.
I equally believe that we're meant to know that "Santa Claus" is Dumbledore. Everything in the Santa Claus notes is entirely 100% consistent with what we know of Dumbledore and his character from canon and from MoR. Likewise, the fact that Mr. Hat and Cloak is entirely mysterious to Zabini and Hermione does not mean that we are supposed to reach deep into the implausible for explanations.
Certainly I could be wrong about any of this. The simple answer is not always the best answer. But all other things being equal, it's a good bet. And the evidence for these "simple" explanations is at least equal to the evidence that, say, Hat and Cloak is a manifestation of Voldemort's essence that leaves Quirrell's body for unknown reasons.
One thing i Just wanted to point out, Mr. Hat&Cloak (or, as Hermione calls him, Mr. Extremely Shifty Guy) appears to shape-shift when talking to her. Has anyone considered that he could be a manifestation of Tonks? Thats a bit far fetched, but whoever he is, he either can shape-shift, OR create illusions to make it look like he does.