Unsurprisingly, the former sandbox maestro (and current social gaming evangelist) had a lot of positive things to say about Facebook. On the other hand, he said that going too far down the accessibility road can lead to "bad art."
He also opined that "design is about constraining people," but that games still have the potential for player creativity, and that Facebook has more user-generated content than games or virtual worlds. If you're confused yet, you're not alone, as Koster also mentioned something about wizards, magic circles, and his belief that the world is becoming more game-like (and thus there's no one better to shape it than game developers). "Let's watch out not to let the pointsification and rulesification, quantification, and reductionism that we have always loved about what we do -- let's not let that change who we are," Koster said.
Check out his notes and slides from the talk via his blog, linked below.