Mark Zuckerberg, Richard Branson, Nilofer Merchant, Clay Shirky, Valentina Rice, Guy Kawasaki, and others know about getting things done, being productive, and keeping a crowd engaged. So when they talk, we should listen. Until the meeting is happily adjourned.
Innovation requires an environment that is open to new ideas. That's all well and good, but innovation is more than blue sky. In order to encourage new and novel solutions, you have to ask the right questions.
Many brainstorming sessions are centered around questions that boil down to "What should we do in response to our competitor’s product or service?" Now the reason you are having the meeting in the first place may be because your competitor has just taken a big chunk of your market share, so that seems like a legitimate question.