StumbleUpon, a fast rising Web search site bought by eBay Inc in May, is moving beyond automated Web discovery to offer a novel way to see what friends find useful or interesting on the Web.

StumbleUpon (www.stumbleupon.com), which has attracted 3.7 million consumers to its easy-to-use thumbs up/thumbs down ratings of Web sites and videos, said on Monday it plans to introduce a new SearchReviews feature on major Web sites.

SearchReviews are available to StumbleUpon users who have downloaded and installed the company's toolbar inside their Web browser. They will start seeing tiny colored icons alongside links their friends have rated.

These ratings will begin running on nine of the Web's most popular Web sites on Tuesday, including any links friends have reviewed on search sites from Google, Yahoo, MSN, AOL or Ask. They also will appear on Google News, Yahoo News, Flickr photos, the Wikipedia online encyclopedia and YouTube videos.

Now you can have a lot of people who have said, 'This is a good page,' as opposed to just ranking the most popular pages, Co-founder and chief architect Garrett Camp said. You can save a lot of time finding interesting things lower down a page.

The review feature will show up on Tuesday to users of the StumbleUpon (http://www.stumbleupon.com/) toolbar. Since its founding by Canadian computer science graduate students six years ago, StumbleUpon users have rated some 13 million sites.

If this catches on and Search Reviews can achieve critical mass, this could change what constitutes popularity on the Web and how we measure it, said Carla Thompson, a product analyst at technology research group Guidewire Group.

But StumbleUpon would have to achieve a much larger base of users before it affects what's popular or not on YouTube.

The ratings system works to personalize the one size fits all quality of discovering interesting links on the Web. Star ratings appear next to Web links or videos, along with icons showing which of one's friends, by name, have rated the site.

We have this database tied to a social network that no one else really has, Camp said. In the future, you can imagine almost any major Web page would have StumbleUpon Reviews.

SearchReviews takes advantage of the ratings that users of the StumbleUpon contribute simply by clicking a button to give a particular site a thumbs up or thumbs down rating. With millions of users already contributing ratings, the utility of these ratings grow the more one's friends use the service.

In effect, SearchReviews layers their own ratings over existing popular sites, with more sites to be added based on consumer demand, Camp said. The colorful but unobtrusive ratings symbols may encourage the user to choose links they wouldn't consider based on their friends evaluations.

To identify their friends, StumbleUpon asks them to allow StumbleUpon to troll through their online address books such as Outlook or Yahoo or Microsoft or Yahoo e-mail to locate other StumbleUpon users. Privacy is assured, company officials said.

Thompson said there is nothing illegal about overlaying additional information onto existing Web sites. Technically speaking, StumbleUpon inserts the additional information in the underlying Web page code with no special effort from users.

The StumbleUpon toolbar is available for Internet Explorer and Firefox. EBay has elected to continue to operate StumbleUpon as a separate company and appears in no rush to integrate the start-up it acquired for $75 million into eBay's auctions, payments and communications businesses.

Eventually, the 19-person company is looking to weave its review features into existing eBay services such as auctions or Skype, its Web-based phone calling service, officials said.

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