I spent a whole day (0900am to 0800pm) in a meeting with just one guy. With a small break for lunch.
You might say that cannot work. You must be braindead after a few hours. No one can be creative that long, and with superior quality. Etc.
But you can! (And you do not even need the iPad App Seth is looking for - even if I like it very much.)
Basically you need fresh air, a fast internet connection, enough water to float your body and brains ...
and a few brains playfully and perfectly complementing each other, passing the ball, adding context, reducing to the max, ...
The magic lies in the two spheres of the brain, challenging each other, the blend of stories and figures, the mix of facts and fiction ... at the level of each brain itself and at the level of the individuals interacting.
The magic lies in concentrating on the meeting, on the task, and vision. Not thinking about all your other activities, meetings, mails. Perfecting the communicative, game-changing interplay of intellect, intuition, and imagination. Just doing it. Knowing you will be at your best when you are truly relaxed and in a laid-back mood. But alert to an unprecedented level to cease every opportunity crossing your mind. It is an intense flow experience.