1) Prof. Quirrell pointed out that Harry was especially vulnerable to the "Finite Incantatem" spell (to removed his transfigured armor). How does the canon mechanics of this spell work from a tactical standpoint? Is it area of effect or targeted on a per spell basis? Can a weak 1st year dispel a casting done by Headmaster Dumbledor or does caster strength play a role in its effectivity? Depending on the answers, Harry's vulnerability could be mitigated by pure strength or recursive spell depth or minor covering spells to absorb the dispelling castings. 'Just saying. :)
As I understand it, Finite Incantatem is an Area Effect spell, while Finite is targeted.
Additionally, strength definitely factors in--again, as I understand it.
edit: Strength has to factor in somehow. Even ignoring the ridiculous unbalancing effect that would have, they're in Hogwarts. If it would cancel every spell in the area, regardless of strength, Hogwarts itself would be affected with every cast.
Haven't really thought about it until now, but I'll assume that Finite is a brute-force method requiring strength proportional to the original spell to cancel (so a Transfiguration that takes minutes would require a mass casting to cancel, perhaps) and sometimes won't work at all, while specialized counter-jinx just works if the caster has sufficient strength to cast it.
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
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. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, 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: