If I was in a Harry Potter fanfic I would probably find out within 3 hours and then spend the next two weeks reading about common plot twists of Harry Potter fanfiction,
In fanfic for almost any universe (whether Harry Potter, Star Trek or whatever) fanfiction devoted to that universe doesn't exist for obvious reasons. So this seems unlikely. Moreover, even if one had almost any fanfic that did have the fictional version of the universe inside that universe also (almost all of which is deliberately silly things like Barry Trotter) there's not much way for you to rule out being a character in the fanfiction- you are random Muggle number 10543549 and you will never encounter any wizards in your life, or if you do, will not realize it. In the unlikely event that you do realize it you will probably be quickly obliviated.
I'm pretty sure Killgore Trout's writings in Vonnegut's books would count. But Vonnegut's universes are hardly typical.
(The HPMOR discussion thread after this one is here.)
The previous thread is over 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 latest chapter as of 09/09/2011 is Ch. 77.
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. 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: