Regarding the subtlety/magic discussion, this is discussed some on YS179. Basically, my interpretation is that it seems to filter down to the idea that a character's emotion-related aspects can be applied to spellcasting. So, for example, Dresden has the aspect "Not So Subtle, Still Quick To Anger". This can be compelled in social environments as normal. In addition to that, though, it could be compelled when Dresden tries to use magic that requires a subtle touch. Generally, Dresden tends to steer clear of such magic because he knows he's bad at it. Likewise, such an aspect could be invoked to boost other sorts of magic. Emotions like anger can feed power into offensive fire spells for example. Dresden does this, from time to time, too.
I don't get the impression that all spellcasters must specialize toward subtle or non-subtle in this way (the section I referenced mentions that "some" spellcasters have "blind spots" of this sort.
That's partially correct. Dresden does have subtlety issues and Molly does have non-subtlety issues. The rules do however explicitly say that you can't make a move action with Evocation because you'd bang into everything along the way. Controlled movement requires more control AKA subtlety than evocation allows. That's a limitation to all evocation not just evocation by wizards with subtlety issue like Dresden. A reasonable inference can be made that if controlled movement is impossible a number of other things must be impossible as well. What inferences can be made is up for debate, but the subtlety limitation on controlled movement is explicit RAW.
Is there an example of a physical skill like Might being used to make a social attack in this way? It feels like something I might do in SotC, but not so much DFRPG. If someone used magic this way, you would roll the Evocation v. Conviction to determine the amount of social stress? My mind is breaking on the amount of social stress you could dole out with a 30 shift thaumaturgical pantsing ritual.
Well there are several reasons you could use to justify limiting or not allowing something like that.
1) To keep beating the subtlety hose: Can you actually depants someone with evocation? Increase the gravitational pull on their pant without increasing it on anything else? Bear in mind that unless they're wearing sweatpants you might not be able to pull their pants down without unbuckling their belt and unbuttoning the pants (or ribbing them).
Leaving the poor horse on the wayside you could also reasonably argue that.
2) It's a maneuver, not an attack, you've depantsed them, congrats, that places the embarrassed aspect on them, but it's not going to scar them for life like 30 mental stress would.
3) Magic generally involves pseudo-latin or gestures. You start chanting pseudo-latin and gesturing weirdly at someone you're having an argument with and their pants fall of and anyone even slightly magic-savvy will do the math. Even someone non-savvy would probably figure it out even if they rationalized it as some kind of trickery. That means that you could easily face the same kind of social consequences from a magical depantsing as from a physical one.
I tend to see magic in social conflicts as requiring a fair amount of justification and being of fairly limited usage just like other non-social skills. Still possible in some cases just like you could use justify Might or Fists in for example an intimidation attempt.