My favorite moment at the Web 2.0 Summit so far happened this afternoon, when Bill Tancer, the global research manager of online research firm Hitwise, described how five months ago, his company predicted the success of seemingly out-of-nowhere chart-topping rapper Soulja Boy.

In case you’re not familiar, Soulja Boy is the auteur of the incomprehensible but highly dance-able song “Crank That,” which has been number one in the Billboard 100 for the past six weeks.

Apparently, Hitwise charted the Soulja Boy boom by tracking the amount of traffic streaming from social networking sites to search engines to his official Web site, and predicted back in May that the rapper (who was virtually unknown at the time) would become a major mainstream success.

“If there’s buzz on the social networks, we track traffic going from those sites to a band’s official web site. Buzz bleeds over to search and you can chart that and see the tipping point in advance,” Tancer said.

Who knew Hitwise was so hip? —Megan Miller