Facebook IPO: Winners & losers

Last December, Zuckerberg donated Facebook shares worth $500 million to the Silicon Valley Community Foundation, a non-profit organization that allocates funds based on the donor's personal interests. The gift is the largest ever received by the foundation, and Zuckerberg said he planned to focus his giving in health and education.

It was the biggest charitable gift to date from Zuckerberg -- who, along with his wife Priscilla Chan, has signed the Giving Pledge, an effort led by Warren Buffett and Bill Gates to encourage billionaires to donate most of their wealth to philanthropic causes.

Zuckerberg effectively gave himself a gift, as well. Charitable donations to qualified organizations are tax deductible. Since Zuckerberg already owed billions in taxes due to the IPO, he may have figured that if Uncle Sam would be taking a large check from him anyway, he may as well hand some of it off to a good cause.

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