Over the last year, as Facebook has exploded in popularity, a nagging question has overshadowed the company: Can founder Mark Zuckerberg and his team make the transition from flavor-of-the-month Web phenomenon to profitable company with a sustainable business model?

After a series of widely criticized missteps—including the company's disastrous launch of its "Beacon" social-advertising platform—skeptics have wondered if Zuckerberg, a 23-year-old Harvard dropout, had the experience and judgment to guide his company to his goal of an initial public offering.

By announcing today that Facebook is hiring top Google sales and operations executive Sheryl Sandberg, Zuckerberg is signaling that he is serious about charting a path to sustainable growth.

"She has just about the most relevant industry experience for Facebook, especially since we need to scale our operations and scale them globally," Zuckerberg told Boomtown blogger Kara Swisher, who was first to report the hire today.

Sandberg, a widely respected tech executive, had been on the shortlist of possible candidates. She becomes the first woman to join the senior management ranks of Facebook.

Zuckerberg reportedly met Sandberg last December at a Christmas party thrown by Silicon Valley venture capitalist Dan Rosensweig, who was once Yahoo's chief operating officer.

Prominent Silicon Valley venture capitalist Roger McNamee then shepherded the courtship—which included a meeting at the World Economic Forum in Davos and several dinners at Sandberg's home in Atherton, California—that led up to today's announcement.

In interviews published today, Zuckerberg acknowledged that Facebook has stumbled recently—notably with complaints that its Beacon advertising system invaded users' privacy. Zuckerberg said Sandberg would bring needed leadership experience to the company.

"Communicating what we are about clearly is an important thing for us to do," Zuckerberg told the New York Times. "We can do that better, and Beacon showed that, as did a handful of other things."

With Sandberg at his side, Zuckerberg can now focus on the monumental challenge facing the social-networking website: justifying Microsoft's decision to invest $240 million for 1.6 percent of the company. The price implied that Facebook had a total worth of $15 billion.

Although Facebook has 66 million users worldwide, the company has yet to come up with a sustainable model to spin a reasonable profit from its user base. (The company currently earns $30 million annually on revenue of $150 million, according to published reports.)

Clearly, Zuckerberg is betting that Sandberg's experience building up Google's advertising platform—which generated the vast majority of the company's $16.6 billion revenue haul in 2007—will pay dividends for Facebook.

Sandberg's pedigree is impeccable: She holds a bachelor's degree (summa cum laude) from Harvard, where she was awarded the John H. Williams Prize as the top graduating student in economics. She then earned an M.B.A. from Harvard Business School, where she was a Baker and Ford Scholar.

After working for McKinsey, Sandberg worked as an economist with the World Bank. According to her Google biography, she focused on eradicating leprosy in India. Sandberg then became chief of staff to Larry Summers during his stint as President Bill Clinton's Treasury secretary.

After George W. Bush was elected in 2000, Sandberg joined Google, becoming vice president for global online sales and operations.

During her six years at the search juggernaut, Sandberg was instrumental in several initiatives, including both AdWords and AdSense. She was also involved in the company's launch of its philanthropic arm, Google.org, where she served as a board member.

In 2007, the 38-year-old Sandberg became the youngest person on Fortune's 50 Most Powerful Women list.

Given how integral Sandberg has been to Google's astonishing rise, the search leader faces a challenge replacing her.

"Sheryl was a valued member of the Google team and we wish her well in her new endeavors," Omid Kordestani, Google's senior vice president for global sales and business development, said in an email statement received by the New York Times.

Kordestani said that David Fischer would succeed Sandberg.

In trading Tuesday, Google shares were down nearly 4 percent, dropping below their 52-week low for the first time since the company went public in August of 2004.