In the next thread Xachariah pointed out that Quirrel likely has possession of the resurrection stone and was very recently(at that point in the story) told by Harry how to identify it. Given Locke's observation in his reply that one of the two privacy spells that have been identified is to detect powerful artifacts it would make sense that Quirrel omitted the spell to detect power artifacts because he had the resurrection stone in his possession. I am not sure why the resurrection stone would be useful for the mission, but surely Quirrel could find something interesting to do with it in that context.
There has also been some speculation that Harry's fathers's rock is the philosophers stone. I am not sure why people would be storing important artifacts on Harry's person, but it would be hilarious to find out that Quirrel stored the resurrection stone in Harry's pouch while he was in there.
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: