Very interesting talk by Christopher Allen at http://www.itconversations.com/shows/detail1072.html
"The Dunbar number is a measure of the cognitive limit to the number of individuals with whom a person can maintain stable relationships. The concept has intrigued sociologists and anthropologists since it was first recognized as the correlation between brain capacity and group size in primates. In this talk, social software observer Christopher Allen discusses the interesting implications the Dunbar number theory has for the gathering of humans on line in the digital age. "
The dunbar number = 150. Number of people in an effective group based on amount of time that you need to dedicate to social grooming.
* Small < 10. Intimate. Good size for chats sessions.
* Medium ~ 100 people. Email lists. Wikis.
* Large > 150. Trust needs to be built into the application. (Eg like slashdot)