Visible Measures points out that while the Seinfeld/Gates clips came out two weeks earlier than the “I’m a PC” ads, Seinfeld/Gates drew twice as many viewers their first week in market than the PC ads did.

After two weeks in market, Visible Measures says, “Seinfeld/Gates was still collecting more than 700,000 views per day, while the ‘I’m a PC’ clips had tapered off to less than 50,000 views per day.”

Why might this be?

Microsoft sparked a dialogue in the Seinfeld ad that isn’t there in PC ads.

“So much viral video is basically word of mouth. And when you build in question into the creative, it gives people something to talk about,” said Matt Cutler, VP-marketing and analytics at Visible Measures Corp.