Christopher Mims comments on a study by Kwak et al. at the Korea Advanced Institute of Science and Technology, who performed a multi-part analysis of Twitter:
"They conclude that it's a surprisingly interconnected network and an effective way to filter quality information.
On the MSN messenger network of 180 million users, for example, the median degree of separtaion is 6. On Twitter, Kwak et al. hypothesized that because only 22.1% of links are reciprocal (that is, I follow you, and you follow me as well) the number of degrees separating users would be longer. In fact, the average path length on Twitter is 4.12.
What's more, because 94% of the users on Twitter are fewer than five degrees of separation from one another, it's likely that the distance between any random Joe or Jane and say, Bill Gates, is even shorter on Twitter than in real life.
Owing to the short path length between any two users, news travels fast in the tweet-o-sphere."