IanB said:
So, if we're giving out free AOOs against inanimate characters, should we not also be letting people take free swings at walls, doors, chairs, evil artifacts, curtains, etc., anytime they want as a free action?
Now I'd be curious why you wouldn't give a character who, in the middle of the fight against his opponent, wants to take a swing at a nearby chair he threatens the chance to waste an AoO on a harmless piece of furniture. I've got to add that I'd view any scene where it makes in-story sense to actually make an attack like that unlikely to turn up in around 80% of the typical D&D game. In any other sense, it's just nonsense, and I never forbid a player to waste his resources on nonsense if he feels like it.
The problem I think is people aren't treating AOOs as an abstraction. That's what they are. They don't handle the case of 'what do you do with a downed character' because that's not what they're meant to handle, and it is just as well, as the game would be unplayably deadly with what people are proposing.
They aren't an abstraction, that's why people are not treating them like one. They are very specifically detailed, what action causes them, how many you get, how to avoid them through feats, and what qualifies as AoO...if you want to call that an abstraction, I guess there's simply different definitions of "abstract" at work in the thread.

An AoO is almost always caused by an action that causes your character to break away from the routine hit'n'parry maneuvers. It also applies to you as long as your opponent thinks of you as an opponent.
For example, if your opponent should successfully manage to trip you, he could in the next round concentrate on another opponent and still smack you when you try to stand up from being prone. That doesn't differ much from you NOT trying to stand up but simply lying on the ground. Your opponent can still side-swipe to smack you one. Even worse, you can't do anything to defend yourself.
The only abstraction in the whole AoO topic is the designers' notion that there should be no "double penalty" to something like being paralyzed. Probably because it would make the game "unfun" at some point. I'm pretty sure if it HAD been done differently, complains about it being essentially "save or die" situations would rank up there with the bodak, death spells, rust monsters and lethal poisons.
AOOs work tolerably well to handle the situations they were designed to handle: providing a balancing factor in caster vs. non-caster combat, limiting the 'infinite chase' scenario, etc. They're a game balance tool more than anything else. For better or for worse, D&D combat is abstract, not a simulation.
That's the basic problem with AoOs, they are too detailed. And, in my personal opinion, a bit silly too. Imagine a fighter who is in melee with an opponent and suddenly turns to the side to swipe at another opponent, who is not really in melee with him, but just did something that threatened an AoO (like drink a potion). Said fighter can do that AoO on the spur of a moment, completely outside his normal attack rhythm, and NOT open himself up to his own opponent? Sounds a tad weird to me, to be honest.
Personally, I prefer to limit AoOs to moments where your character REALLY opens himself up for an attack...spellcasting, certain magic item use, running past (or away from) an opponent without some kind of preparation, rummaging in your backpack for some item. Stuff like that. Everything else is basically a combat action that shouldn't carry much of a penalty, really. I simply don't believe that a combatant opens himself up that much when he tries to disarm his opponent, for example, or tries to trip him. I've seen too many combat schools with specific in-combat maneuvers for exactly that kind of thing, unarmed and armed, doesn't matter. They simply are metagame constructs that end up punishing creative combat maneuvers more than older-edition "there are no real rules for it" ever did.
One thing that was mentioned in this thread a few times sounds like a viable alternative...have all those actions that "leave your character open" simply leave him flatfooted for that round, unless he does some "casting on the defensive" or equivalent check to avoid that. It's punishment enough in a lot of cases (since many high-damage abilities are based on an opponent losing his Dex bonus to AC), and doesn't grant an attacker a sudden, out-of-the-blue additional attack.