Perception of Yahoo among U.S. adults has fallen steeply since the company kicked off its global campaign centered on the tag line "It's You" on Sept. 28, based on YouGov's BrandIndex, which tracks daily consumer perception of brands. It found Yahoo's buzz score had tumbled from 35.4 on Sept. 22 to 25.5 as of Monday.

Regarding Yahoo, people were asked if they had "heard anything about the brand in the last two weeks, was it positive or negative?" YouGov said the 10-point drop follows a steady climb in the Web portal's index score from mid-May through most of September, and marks the biggest plunge Yahoo has had all year.

BrandIndex scores are based on interviews of 5,000 people each weekday from a representative U.S. population sample of 1 million. A score can range from 100 to -100, and is compiled by subtracting negative feedback from positive. A zero score means equal positive and negative feedback.

"There's been a lot of buzz leading up to the campaign, and when it finally broke, maybe a bit of a letdown," said Ted Marzilli, senior vice president of BrandIndex, offering a possible explanation for the sudden drop in Yahoo's score.

The company's global "It's You!" campaign, spanning TV, online, outdoor and other media, is intended to emphasize the increased personalization Yahoo offers following its home page redesign and addition of features giving users greater ability to customize the site.

Yahoo's "Anthem" TV spot features a series of eye-catching images, from a woman shooting rose petals out of a gun to kids kicking a soccer ball across world capitals to people gyrating on a crowded dance floor.

Marzilli said he himself found the initial spot visually impressive, but not necessarily effective in communicating how Yahoo is different now than six months or a year ago. "There just seems to be a bit of disconnect between consumers and the campaign," he said.

The rebranding effort developed by Ogilvy & Mather and Landor Associates has drawn similar reaction around the Web. A dozen comments posted on AdAge.com asking about the TV ad when it launched were mostly negative.

"Yes it is a lot of glitz and glamour, and I am aware that 'something" is coming that is all about "Y!ou' but I have a hard time believing Yahoo! will be able to live up to the hype they are creating in this ad,'" read one post.

The campaign also includes online and outdoor ads featuring a diverse range of actual Yahoo users and lines such as: "The Internet is under new management, yours," "This time it's personal," and "Totally, you."

For its part, Yahoo said it’s already gotten positive feedback from consumers, advertisers and partners in response to the campaign. “We view our brand revitalization efforts as more of a marathon, not a sprint, so we're focused on the long-term trends of Yahoo!'s audience size and user engagement metrics,” read a company statement.

To help reinforce the focus on personalization, Yahoo Tuesday announced a competition allowing people to submit their own versions of its signature "yodel" audio tag to a specially created site through Nov. 8 for a chance to be included in the global ad effort and featured on the Yahoo home page.

Yahoo Tuesday also set up one-day temporary recording studios in Times Square in New York, London and Mumbai with celebrity hosts to encourage people to enter the yodel contest. While Yahoo's brand perception score may have dropped sharply, Marzilli noted that it's still higher than rival portals such as AOL (-7) and MSN (3), but lower than Google (42).