The study of social influence, by Duncan Watts of Columbia University, shows that most-popular lists, the common feature of social media sites, make hits bigger, because users look to eachother's choices as an indicator of quality. A law of cumulative advantage, in which the popular becomes more popular, applies. But more important is his conclusion that the outcomes are erratic: it's not simply that audience gravitates to the best tracks or news headlines; like any herd, its course appears chaotic.

In one controlled test in Watts' experiment, the song 'Lockdown' emerged as number one song; in another similar group of users, it ranked only 40th. So what's the lesson for any producer of content, or service, for that matter, on the internet?

The early adopters are even more important than one thought: regardless of a product's intrinsic merits, an early signal of popularity can make all the difference. Which helps explain why we're all obsessed by Technorati rankings, for instance. The initial support of a small group of influencers, as savvier publicists already know, is critical even to mass-market products.