(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Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).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.
Harry leaps to that conclusion before hearing from Dumbledore how difficult they are to create. Even if that was the method, there is still the question of how they managed to accomplish it.
My hypothesis — as of several chapters ago — is that Dumbledore assisted in the Rita prank. He certainly had the motive, since he's playing the game against Lucius and Rita was Lucius's pawn. He also had the means (being incredibly powerful). Why hadn't he acted against her earlier? Because he hadn't been clever enough to think up a good way to get at her without inviting retaliation.
So how did he ever get included in the twins' plan?
Easy: he's in the habit of routinely reading their mind. Evidence for this lies in chapter 63: "It wasn't that the Headmaster had popped up out of nowhere and was staring at them with a stern expression. Dumbledore was always doing that." There's also weak evidence in chapter 12, where Dumbledore knows Harry wants to reformulate Quidditch (he could know via F&G via Ron). And in chapter 79, where he knows about the map.
So: The twins are walking around thinking about how to implement their plan against Rita, Dumbledore pops up out of nowhere looking for some good gossip, sees their plans, seizes the opportunity. The exact implementation could either be a memory charm (maybe trap her when she shows up at Mary's room looking for gossip about Amelia Bones, Dumbledore's ally), or else Dumbledore could actually pull off the acts Quirrell calls impossible.
Hold on - didn't Lawful Good Dumbledore make a big deal earlier in the Snape fight that he didn't invade student's minds?