At just 38 years old, the former VP of ad sales for MTV Networks became one of Microsoft CEO Steve Ballmer’s top lieutenants (and one of few women in those ranks). Ballmer has been vocal about expanding Microsoft’s advertising business to account for 25% of overall revenue. For Everson, that would have meant taking ad sales from $3.3 billion to $15 billion across the company’s divisions, from the Xbox video game business to the Windows Phone 7, launched last year. Facebook’s ad revenues are reported to be close $2 billion, and growing fast.

Everson declined to comment to Fortune about the job change. But in an interview last September, Everson said she had joined Microsoft because “there are only a few seats at the table to change the [advertising] industry.” It’s no secret that Facebook is one of the biggest players at that table.

Although Facebook is headquartered in Palo Alto, Calif., Everson is likely to remain in the New York City area (and close to Madison Avenue). It was a concession she pushed for in her negotiations with Microsoft, so that her family could remain in New Jersey, where she grew up. She has quite the brood; in addition to twin daughters, Everson cares for a menagerie of pets that includes three dogs, a guinea pig, a rabbit, and four frogs.

Back in September, Everson said was cautiously optimistic about the economic recovery in the U.S., and concerned about the unknown: “Do we really understand this new economy that’s so global and tech focused?” With a move to a company that is at the center of the digital universe and has more than 500 million members around the world, Everson is now in a position to learn all there is to know.

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