PALO ALTO, Calif. — As Facebook.com's mastermind, Mark Zuckerberg is sitting on a potential gold mine that could make him the next Silicon Valley whiz kid to strike it rich.

But the 22-year-old founder of the Internet's second largest social-networking site also could turn into the next poster boy for missed opportunities if he waits too long to cash in on Facebook Inc., which is expected to generate revenue of more than $100 million this year. The bright outlook is one reason Zuckerberg felt justified spurning several takeover bids last year, including a $1 billion offer from Yahoo Inc.

"We clearly have a bias toward building than selling," Zuckerberg said in a recent interview. "We think there is a lot more to unlock here."

The build-or-sell dilemma facing Zuckerberg is becoming more common among the precocious entrepreneurs immersed in the latest Internet craze, a communal concept of content-sharing that has been dubbed "Web 2.0."

Besides Facebook, other Web 2.0 startups frequently mentioned as prime takeover targets include online video site Metacafe Inc. and Photobucket Inc., which has emerged as one of the Internet's busiest destinations by hosting personal videos and photos that are routinely linked to top social-networking sites like MySpace and Facebook.

These sites find themselves at a critical juncture reached several years ago by the Internet's first big social-networking site, Friendster.com, which chose to stay independent instead of selling. That decision is now regarded as one of Silicon Valley's biggest blunders.

Web 2.0 startups have emerged as hot commodities because they are drawing more people away from television, newspapers and other media traditionally used for advertising. Online video channels and social networks, a catchall phrase attached to sites that enable people with common interests to connect and deepen their bonds, are particularly hot.

Deep-pocketed companies are now angling for a piece of the Web 2.0 action — a quest that already has yielded a couple big jackpots, helping to propel the sales prices of startups to their highest levels since the dot-com boom.

News Corp. paid $580 million in 2005 to buy MySpace, the largest social-networking site, and Google Inc. snapped up video-sharing pioneer YouTube Inc. for $1.76 billion late last year.

"I'm surprised a lot more companies haven't already been bought," said Reid Hoffman, a veteran Silicon Valley executive who has invested in many startups, including Facebook. "My hunch is the deals are only going to get more expensive in 2008 and 2009."