Web 2.0 websites accounted for 12 percent of all U.S. internet traffic, according to recent findings by online intelligence firm Hitwise.

Hitwise General Manager Bill Tancer told a gathering at the O'Reilly Web 2.0 Expo that the market share of visits to Web 2.0 sites has grown 688 percent over the past two years.

According to Tancer, sites such as Wikipedia, Flickr and YouTube are dominating the Web 2.0 landscape.

"Web 2.0 websites like YouTube, Flickr and Wikipedia have achieved mainstream adoption for visits to their website," said Tancer. "It's the participatory aspect of Web 2.0 that is still in a very nascent stage. When online participation goes mainstream, we can expect an explosion of new content on the web."

Tancer said Yelp, StumbleUpon, imeem, Veoh, WeeWorld and Piczo are positioned to be part of the next wave of popular Web 2.0 sites.

Early this year, Time Magazine relaunched Time.com with an increased commitment to Web 2.0 features.