Free Money's Always Good, Right?

According to the Wall Street Journal, Bill Gates and Warren Buffett are pretty darn persuasive.  They've convinced over 40 people, mostly billionaires, to give half of their fortunes to charity.  The project is called the Giving Pledge and was announced by Bill and Warren about a month and a half ago.  Of course, these people aren't legally obligated in any way to give up their cash, but they've publicly said that they're going to, so I don't think they'd want the bad publicity of backing out.

You can argue all you want about the usefulness or uselessness of charitable organizations, but I think it's fair to say that giving away a few billion dollars can't be a bad thing, can it?