I've always been a little suspicious of groups and how they work together. Probably a result of my being an only child, followed by a few frustrating experiences with group projects in school and grad school. But experts who study this sort of thing have actually taken group dynamics apart and have learned what makes for good collaboration.
This issue is thoroughly explored in Group Genius: The Creative Power of Collaboration by Keith Sawyer, Associate Professor of Education and of Psychology at Washington University in St. Louis, the author of six other books on creativity, and a corporate consultant on creativity. Group Genius is a pleasure to read, relevant, practical, and inspiring, both for those with a background in creativity studies and for those most focused on creativity's applications in the marketplace.
TWO THINGS I LEARNED:
1. More diversity in a group leads to more group flow, while it avoids groupthink and conformity.
2. (And this was a shocker) Better ideas come out of a brainstorming group when its members are told explicitly to be more imaginative, unique, and valuable. In other words, when brainstorming, don't turn off your critical faculties entirely, but don't focus on what you think will work, about what has worked before, or about what is familiar.