Warren Buffett (L) and Bill Gates.
Warren Buffett (L) and Bill Gates. - 
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Tess Vigeland: Mark Zuckerberg, Warren Buffett and Bill Gates have many things in common, not least of which is the fact that their wealth is tallied in billions. They've also signed a pledge to give away the majority of their money. Zuckerberg and 16 other billionaires are among the newest to sign onto the effort.

Marketplace's Jennifer Collins looks at what they're really pledging and what it buys them beyond the PR buzz.

Jennifer Collins: Let's face it, Facebook CEO Mark Zuckerberg could use a little good PR right now. Since he's not always done so well with the ladies, at least according to the movie about him.

"The Social Network": You're going to go through your life thinking that girls don't like you, because you're a nerd. But I want you to know from the bottom of my heart that that won't be true. It'll be because...

We scratched that next word. So maybe Zuckerberg's joining something called the Giving Pledge to generate nicer words about himself. Billionaires Bill Gates and Warren Buffet launched the effort to get the super rich to give away more than half their wealth. But much of this wealth is tied up in investments. So how real are these pledges?

Betsy Zeidman: Probably 100 percent of it is not real because much of it is paper money.

Betsy Zeidman is a senior research fellow at the Milken Institute. Her chairman, Michael Milken, who made a fortune off junk bonds, also signed onto the pledge.

Zeidman: But I think that even if it isn't all real, ultimately, it is still a significant amount of money.

Daniel Borochoff at the American Institute of Philanthropy says much of the money will go to private foundations that only have to give out about 5 percent of their endowment a year.

Daniel Borochoff: So this may not be helping out as much as we'd like to think this is helping out.

But one thing's for sure, these donors won't end up in the poor house. If Warren Buffet, for one, gave away 99 percent of his wealth, that would still leave him with a tidy $450 million.

I'm Jennifer Collins for Marketplace.