] The world has known about the small-world phenomenon
] since sociologist Stanley Milgram's 1967 study found that
] it took, on average, six exchanges among acquaintances to
] get a letter from a random correspondent in Omaha,
] Nebraska to a Boston recipient identified only by a brief
] description.
] ...
] Columbia University researchers have filled in the blanks
] by carrying out a larger, more detailed experiment over
] the Internet. The results match many of the broad
] conclusions of Milgram's work, but show that Milgram's
] conclusion about the importance of hubs -- people who
] have many connections -- may be off, at least in regards
] to social networks.
]

It turns out that social networks do not behave like the scale-free networks exhibited by web page linking. There is a cost to participation in a social network. Folks with fewer connections were more likely to pass on the message.