Another interesting document about creativity (which echoes the one from John Cleese), by Isaac Asimov. It is not about Game Design (neither was John Cleese’s lecture), but all these tips/advises are very useful for a group brainstorming activity.
http://www.technologyreview.com/view/531911/isaac-asimov-mulls-how-do-people-get-new-ideas/
Version française