Let's go in reverse order, actually. Check under the fold for the porny-bits.
Functional Programming: I finally "got it" earlier today. Watching a video, I finally grasped why people care - not in some abstract "it's purer" sense, but in a "I can write programs better" sense.
Basically what I realized was that I'd implemented, haltingly and uncertainly, certain aspects of functional programming in the game, and that those parts were both elegant and comprehensible at the same time. If any backers care about code, open up game/people.js, line 63. Action.choosePerson is, in a hacky sort of way, curried Game.checkConditions.
In fact, the whole checkConditions mess (it's by far the hairiest part of the game engine - see /engine/modules/classes/conditions.js) could be rewritten much more elegantly using functional programming. I doubt I'll do that, at least not immediately, but it finally clicked.
Pure functional programmers are still crazy. :P Mutable state is the way both the real world and actual computers operate.