When Yahoo announced in July that it had hired 37-year-old Marissa Mayer as its new CEO, you could practically feel the double takes happening all over Silicon Valley. Nobody thought the troubled Web company could snare an executive as well respected as Mayer, Google's 20th employee and a key contributor to its success. She has yet to put her imprint on Yahoo aside from some small deals, like an agreement to put content from Wenner Media's Rolling Stone and Us Weekly on the site but her mere presence has boosted its reputation. And the fact that she gave birth to a baby boy weeks after taking the job has made her the Fortune 500's highest-profile working mom.
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