Nielsen surveyed Internet users in 47 markets in Europe, Asia Pacific, the Americas and the Middle East on their attitudes toward many types of ads, including television, branded Web sites and consumer-generated content.

"The fact that consumers think opinions posted online are as trustworthy as brand Web sites speaks to the power of online reviews and recommendations," said Debra Aho Williamson, senior analyst at eMarketer.

"It also means that marketers need to focus as much attention on what consumers say about their brands online as they do on creating the brand Web sites themselves," Ms. Williamson said. "The easiest thing to do is to make consumer feedback an essential part of every brand Web site."

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