Double magic may be a reference to Grossman's The Magicians. Warning: While there are many good things in the book, the viewpoint character is depressed and (in my experience) depressing.
I don't know whether Grossman has read HP:MOR, but he heads it off at the beginning of the book. Everyone at the magic school is a good bit smarter than average, but there's no one who's qualitatively smarter than that, and it's stated that enough unproductive research has been done into the roots of magic that it's generally considered to be a dead end.
Grossman's novel was written in 2009. So barring time travel, he wrote his novel before encountering HPMR if he has encountered it.
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
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. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
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: