I learned how Attacks of Opportunity worked from Eric Noah's site before 3e was released. He even had some examples of how what was known of the rules worked in play.
By the time the game released, those of us who had been following along already knew how to play it. Then, people started complaining about how difficult AoOs were to understand (which, frankly, I didn't understand--they're really not that complicated).
between reading the rules and see Eric's explanation, was sufficient.
Frankly, every old-timer on this site should KNOW the AoO rules because of that demo.