So I checked out some of the references at the end of Malcom Gladwell's The Tipping Point. Mostly because Gladwell's books always leave me feeling enthusiastic about their ideas, but with the desire to put my hands on something concrete. I became interested in work by Schelling on peoples self segregation. It wasn't so much that the model was surprising from a sociological or mathematical standpoint, but because it represented a pretty simple idea which could be applied to Processing. :-)
So, here it is: more art than science, my processing app which represents a world of households who are just looking for a place to land. They definitely prefer living near each other rather than in isolation. However, if the neighbors are too different from them they will definitely be looking for a better place to live. You can adjust the tolerance of the people that live in the world. See what happens if they become very tolerant quickly vs. slowly, or what the effect of slowly reducing tolerance for a very stable world is. Can you find the tipping point at which order starts to form from chaos?