John Allen Paulos in his Who’s Counting column at ABC News:
Whether about blogs, songs or news stories, when people must make decisions among many different alternatives, those making them later are often greatly influenced by those making them earlier.
That creates a cascading effect that results in a “popular-get-more-popular” sort of phenomenon along many different dimensions.
This is one reason so-called power law distributions are so common in social situations.
In particular, such power law dynamics partially explain the fact that a few blogs are visited by millions, while the vast majority are lucky if they attract the bloggers’ close friends and relatives.