As more people put their own content online, tagging is becoming an increasingly popular Internet search tool.

Now marketers and even retailers are starting to recognize the value of tags, which allow consumers to not only organize content under a certain keyword but also share it with others.

"The real goal of tags is to allow people to find what they are looking for quickly," said Jeff Block, vice president of community development for Oak Brook's Capable Networks. "It's the user categorizing the content."

Tags are a staple at so-called Web 2.0 sites, those where people create and upload content. For example, after creating an account on a site like Flickr.com, you can upload photos to the site and then label the photos in a way that makes sense to you. Labeling a photo of Tower Bridge as "London" allows anyone using the Flickr's search function to find your photo and other photos that are similarly named.

At Technorati.com, a site that compiles blog posts and other content, tags have become an integral part of the home page. They help Web surfers, at a glance, see popular topics. If you click on a "Sopranos" tag at Technorati, for example, you will be directed to blog posts, video clips and other bits of content that have flooded the Web in the wake of the controversial ending to the long-running HBO series.

About two-thirds of the information that is currently discovered by Technorati users is through tags. The rest comes from keyword searches, the technique the company started with in 2002. A December survey by the Pew Internet & American Life Project found that 28 percent of Internet users have tagged content online such as photos, news stories or blog posts.

"People are being bombarded with information," said David Sifry, Technorati's founder and chief executive officer. "So we are reacting by how to organize this. If you want to get to the good content, you can take advantage of the categorization of stuff that other people are doing."

Social groups form

Tagging not only lets consumers organize the vastness of the Internet in a way that makes sense to them, but also "allows social groups to form around similarities of interests and points of view," David Weinberger, a fellow at Harvard University Berman Center for Internet & Society, told Pew. "If you're using the same tags as I do, we probably share some deep commonalities."

It's that social aspect that interests advertisers, who see tags as way to expose what are essentially self-selected, targeted audiences to their products.

Block, of Capable Networks, said "in and of itself, there's not much marketing value to tags, but they can be used to keep people at a site." Capable develops community Web sites for consumer electronics gadgets.

"If companies are smart, they are observing the democratic interaction of the community and learning from it," Block said.

At Technorati, tags now are sold. The site began in January to sell advertising opposite popular tags, much as Google puts a price on popular search terms.

"Advertisers love the ability to have highly relevant information for people associated with their product," Sifry said. "We can target ads based on the tags. So if you type in 'auto show' you should get car ads."

The site also sells "bundles of tags," he said, meaning advertisers can buy a category of tags, such as entertainment, technology and travel, since it is unclear when a particular tag could become hot.

"At any given moment the content can change, suddenly and dramatically," said Derek Gordon, Technorati marketing director. "One day it may be all about the fall prime-time television lineup, and the next day it could be about Paris Hilton going to jail."

For example, if you click on the tags "music" or "iPhone" at Technorati, an ad for Microsoft's Zune digital music player appears next to the content links. If you click on a "Sopranos" tag, an ad for Verizon's Internet service emerges.

The flexibility to buy a tag within a group -- "Sopranos" would be entertainment -- has "been great because we have advertisers who want to be more targeted but not miss when something big happens," Sifry said.

And with tags it's easy to tell when something big happens.