I would add as weak evidence the need each person has for being Mr-Hat-and-Cloak.
Hermoine Granger recognizes the true face of Mr-Hat-and-Cloak. This should rule out proxy agents or Sirius Black.
I don't think Sirius Black can be ruled out. It's quite possible that Hermione has seen pictures of famous past criminals, including Sirius and Bellatrix. Also her sudden terror at recognizing him seems way bigger than if it had been someone like Severus or Quirrel, so this recognition made me update upwards the probability of him being Sirius Black, not downwards.
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: