Plane Sailing
Of course, nobody has yet mentioned some of the wonky things about AoO <edit>
AoO are an imperfect solution to a particular problem. They are one solution amongst many imperfect solutions. <edit>
It would be well for some of the pro-AoO crowd here to recognise the truth of this.
I have no problem with admitting any of that. No rules system is perfect- I just happen to like AoOs in D&D 3.X.
For every rule created, there will naturally arise unintended consequences, usually because of the interaction of rules that were not contemplated in the creation of the first rule. Some of those unintended results are going to be insignificant. Others will result in things wildly at odds with the internal logic of the game, or the reality the rule was meant to model.