PsyBlog looks at ten studies that bear out rules of thumb for predicting group behavior. One is that that gossip is inevitable and, on the whole, quite accurate:

Simmons (1985) analysed workplace communication and found that about 80% of the time people are talking about work and a surprising 80% of the information was accurate. Other studies have come up with a similar figure, suggesting that while details are inevitably lost along the way, the grapevine is mostly accurate.

Others include how leaders emerge from groups of conformists, people take their assigned roles seriously, and how groups become closer as they become more exclusive.