From his 24th-floor corner office in midtown Manhattan, the veteran CBS research chief David Poltrack can gaze southward down the Avenue of the Americas, its sidewalks teeming. For more than four decades, it has been his job to measure people's television habits, preferences, and reactions. In large part, this has meant following the viewing habits of Nielsen panels of TV viewers and parsing the results of network surveys on their opinions. On a late September afternoon, with fall premieres under way, his desk was strewn with color-coded opinions from 3,000 Americans who had wandered into CBS's Las Vegas research outpost, Television City, at the MGM Grand Hotel and Casino, and agreed to fill out TV surveys for the chance to win a 3-D home entertainment system.

But now he's also dealing with a growing force: the masses talking back through social media. Of the approximately 300 million public comments made online worldwide every day—about two-thirds of them on Twitter—some 10 million, on average, are related to television (though daily numbers vary quite widely). "¿Que sera two and a half men si[n] Charlie?" one viewer recently tweeted, alluding to the replacement of Charlie Sheen by Ashton Kutcher on the CBS sitcom. "The beginning of Person Of Interest is like Jack&Ben all over again," remarked another. (A couple of weeks later, another added: "I assume CBS will keep going with what's been working for them, and replace Andy Rooney with Ashton Kutcher.") TV executives like Poltrack must now grapple with these spontaneous, messy, irreverent remarks.