Sorry, I'm really not following your pie argument. Harry would learn about the pies in the near future; since it is his style, he would think about throwing them to frighten the bullies. So, his observation of Harry+1 throwing the pies is not necessary for him to think to throw pies anyway.
What do you mean by "they don't recurse"? Surely the fact that this procedure results in fast graph isomorphism testing shows that it is not a particularly "stable" solution? Or, do fast integer factorization by writing down the first digit for the least factor greater than 1, listen as future you says "no, no, maybe," and change it to whatever, and then figure out the second digit, and so forth. The scenario you've outlined results in nearly instant integer factorization (or password guessing, or whatever), so it is probably illegal.
Note that both graph isomorphism and integer factorization are problems that may well lie in P, so these aren't great examples. Traveling salesman is a bit better.
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: