Jake Song - a superstar yet down to earth and open Korean programmer - shared his long experience of building online worlds, first in 2D (Lineage, Ultima Online) then in 3D (Lineage 2, World of Warcraft). His talk resembled a how-to build the perfect virtual world, and my favorite slide was the one that said "try to build a weird enough world so users feel like they are somewhere else, but simple enough that people can still use common sense".
This talk was given in Korean and translated live in English for the conference participants. Unfortunately we could not record the English audio.