The University of Milan and Facebook have finished a research on the theory of six degrees of separation. It was based on the social graph of Facebook. There have been investigated all Facebook accounts. It turned out that any two people are 4.74 steps away (not 6 steps), by way of introduction, from each other on Earth.
By the way, in the U.S. the number of chains is less than 4.37 (statistically, Facebook is used by more than half of Americans in the age of 13 and older).
The researchers said, "Even if we take the most geographically remote Facebook user in the Siberian tundra or the Peruvian jungle, a friend of your friend probably knows a friend of a friend".
Three years ago, Microsoft made a similar research of 242 million MSN users that had written at least one message per month. Their result was equal to 6.6.