In 1967, a young psychology professor named Stanley Milgram, sent 300 identical letters to randomly selected people in Omaha, Nebraska. Each letter requested its recipient to forward the letter to a lawyer in Boston. Armed only with the Lawyer's name and the city he lived in, the recipients were told that if they didn't know how to reach the lawyer directly, they can send the letter to someone they think will have a better idea - a friend or a family member perhaps.

The ramifications of Milgram's experiment, and the "Small World" theory behind it, are only now starting to make an impact.

In 1999, a relatively unknown writer by the name of Malcolm Gladwell, wrote an article in the New Yorker titled "Six Degrees of Lois Weisberg". In his article, Gladwell argued that Milgram's "degrees", the links that connect us to each other, aren't equal. In fact, some links are a lot more important than others. Some people are far better connectors than other people. Gladwell then went on to tell the story of Lois Weisberg, a chain-smoking, serial-coffee-drinking grandmother from Chicago. Lois seemed to know everybody. And everybody who knew Lois agreed that if you want to get in touch with someone you don't know, chances are Lois can make the connection.

A year later, Gladwell published one of the most influential books in recent times. "The Tipping Point" argued that products, ideas and messages sometimes behave like diseases. More specifically, they behave like outbreaks of diseases. The nerdy-looking shoes that suddenly become a must-have fashion item, the unknown writer who's novel suddenly becomes a best-seller, a sudden rise in teenage pregnancies--are all what Gladwell calls "social epidemics".

Take SARS, for example. Why does a disease that infected less than 8,000 people and killed less than 800 receive so much attention, when other diseases kill more people, have a higher mortality rate and are a lot more infectious? The reason, as Columbia sociologist Duncan Watts explains, is that the World Health Organization decided to focus on SARS very early on, engaging the media in what became the most extensive coverage of any disease since AIDS. Oddly enough, argues Watts, the fact that SARS has become a "social" epidemic ensures that the disease probably won't spread as fast and as far as it could have. By acting early and telling the media a good story, the WHO managed to create a widespread panic that may have saved thousands of live.

So what's that got to do with you? If Milgram and Gladwell are right, then not only are we all interconnected, but some connections are a lot more important than others. If you're launching a new product, for example, you don't need to reach all of your target audience, just those people who have the influence over the most connections. The trick, of course, is to find who these people are. Linked-in, a new online service, may have solved that problem. Linked-in asks you to sign up and invite your friends to form your "Network". When they sign up, their friends become your friends.