EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
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. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
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, ten.
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Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).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.
My mental model of Lucius says he believes...
Harry is Voldemort (Who is still strong in some ways but weak in others)
Harrymort has been trying to split Draco from his father.
Harrymort has been using a new ideology to recruit Draco.
This new ideology is incompatible with the previous ideology.
Harrymort has no use of his old allies as he hasn't let them in on anything and he's using an incompatible ideology.
Harrymort's gathering of power and allies/minions (eg Hogwarts students) will take at least a decade to come to fruition.
Harrymort is in a weak position right now and in danger of losing a key piece. (Hermoine would be his Bellatrix.)
Harrymort seems to be on Dumbledore's side in the court room and ideologically.
So, assuming Lucius isn't just acting on rage, he's decided to align himself against Harrymort and with whoever it is that's attacking him. Perhaps he's hoping that he can destroy Harrymort soon enough before he becomes invincible withe the passage of years. Perhaps he hopes by aligning the House of Malfoy against Harrymort publicly, whoever attacked his son won't target him again and risk losing the Malfoy's support. Perhaps he thinks Harry is strongly allied enough to Dumbledore to lie to Lucius. Although I'm more of the mind that he's acting on blind revenge, or at least it's clouding his vision enough to make poor choices at the moment.