MENLO PARK, CA—Dawn breaks across San Francisco Bay, and on this brisk April day the only sound disturbing the morning quiet is the steady clip of a sleek two-person skiff as it glides along the inlet toward the heart of Silicon Valley. Observing this tranquil scene, one would never suspect that the two young men cutting through the water are none other than Cameron and Tyler Winklevoss, twin brothers and co-founders of HarvardConnection, the ubiquitous and seemingly unstoppable social network site that, according to industry estimates, is valued at a staggering $400 billion.

Expertly negotiating the contours of the bay, the Winklevoss twins guide their watercraft to an expansive dock abutting “The Boathouse,” HarvardConnection’s sprawling Menlo Park waterfront campus, which serves as both a place of business for 20,000 dedicated employees and a powerful symbol of all the brothers have accomplished.

These luxurious environs, where hundreds of programmers are dialed in coding, encapsulate both the history and the bright future of the most prominent force in social media, a chronicle made possible by the two boatsmen currently disembarking their vessel and preparing for yet another day of changing the world—two brothers who were never afraid to row against the current.

“From the very beginning, we knew we had seized on something special, but neither one of us could have imagined the site would take off the way it did,” says Cameron Winklevoss, who with his brother has grown HarvardConnection, a universally beloved internet hub that allows web surfers to create personal profiles and virtually connect with friends and family, into a social media juggernaut that today counts more than 1 billion users worldwide. “It’s hard to believe that all this came out of what we hoped was a cool million-dollar idea.”

“Turns out a billion-dollar idea is even cooler,” Cameron added with a slight grin.

As the 31-year-old brothers explain, their groundbreaking social platform originated in 2004, when the self-styled “gentlemen of Harvard” were a pair of ambitious undergraduates with a vision that would eventually come to revolutionize how people interact online.

The site was the first of its kind: a virtual meeting place that allowed Harvard students to upload and share photos, web links, and personal messages, creating a vast social network unlike anything seen before. In its nascency, the siblings say HarvardConnection—known in its early days as The HarvardConnection—already showed great promise, even before it emerged as the definitive cultural phenomenon of the 21st century, and well before “Winklevoss” became the household name it is today.

“Within hours of the launch, HarvardConnection had taken our college by storm, and things just took off from there,” remembers Tyler Winklevoss, who this year was dubbed one half of Forbes Magazine’s “Twin Towers of Social Media,” and who, like his brother, has accumulated a personal fortune estimated at well over $20 billion. “It wasn’t long before we were opening it up to Yale, Columbia, and Stanford. We got the Boston University student newspaper to plug it and it took off at BU, too. And by then we knew: We had to go to California to round up investors and work on the site full-time.”

“Aside from a little coding work from a fellow Harvard student in the very beginning, we built it all on our own, just the two of us,” Tyler adds. “I mean, this was a once-in-a-lifetime idea, and one we knew we had to keep to ourselves. We’re not idiots.”

Nearly a decade later, the fruits of the brothers’ labor can’t be missed. As co-CEOs of HarvardConnection Inc., the two have expanded their modest dorm-room venture into an imposing Silicon Valley blue chip that dominated former competitors MySpace and Friendster and now rivals such tech industry heavyweights as Apple and Google in sheer size and influence. And this has translated to unfathomable profits for the twins and their investors.

After early issues following their initial public offering, the sibling tech pioneers are back and ready for any challenge.

Additionally, with the time they don’t devote to growing their web 2.0 empire, the Winklevoss twins have cultivated enviably lavish lifestyles that include a shared top-floor penthouse in San Francisco’s swanky North Beach neighborhood, a luxurious residence that just happens to be paddling distance from work. And it should be mentioned that even helming the world’s most successful company hasn’t distracted the brothers from their prodigious crew careers; most notably, they rowed for the U.S. in the men’s coxless pair at the 2008 Summer Olympics in Beijing, where, as usual, they left the bulk of the competition in their wake.

But in spite of their impressive accomplishments, both brothers emphasize the importance of staying humble.

“The scope of what we’ve done still astounds us,” says Cameron, claiming that the resultant fame and financial success is eclipsed by the satisfaction of creating something for which they will never be forgotten. “HarvardConnection truly changed the world. Nobody can take that away from us.”

“We can’t let it get to our heads, though,” adds Cameron, as the twins enter the Boathouse, the challenges and rewards of another exciting day lying ahead. “Technology evolves. Currents shift. And that’s why we’re still out on the water every morning. Whatever comes next, we’re planning on making a splash.”