Harlan Ellison ofter wrote short stories in a storefront using ideas tossed out by on-lookers. I'd love to see the programming equivalent, particular in the game space. It'd go a long way towards settling the art versus science debate--and I doubt there are but a handful (including Notch) who could perform the kind of improv that someone like Ellison did in his medium.
Recently I attended a gathering where about ten people tossed out ideas for an interactive fiction game as it was being live-coded in Inform 7. It was surprisingly fun (and if we had a better grasp of the language it would have been even more).
