The smallest, three to five, is a "clique": the number of people from whom you would seek help in times of severe emotional distress. The twelve to 20 group is the "sympathy group": people with which you have special ties. After that, 30 to 50 is the typical size of hunter-gatherer overnight camps, generally drawn from the same pool of 150 people. No matter what size company you work for, there are only about 150 people you consider to be "co-workers." (In small companies, Alice and Bob handle accounting. In larger companies, it's the accounting department -- and maybe you know someone there personally.) The 500-person group is the "megaband," and the 1,500-person group is the "tribe." Fifteen hundred is roughly the number of faces we can put names to, and the typical size of a hunter-gatherer society.

Interesting look at group dynamics. Explains why I feel most of "the company" are soulless whores whose job is to tell me "no." ;-)

Schneier on Security: Security, Group Size, and the Human Brain