Personally, if I had all that money I would not give it to charities, or if I did, then only to the ones that invest in R&D for renewable energy, or cancer cures or something that feels like progress.
In fact, I would make science a top priority. Giving the money to people like the mother of Precious seems like a waste to me.
Warren is obviously free to do whatever he wants with his money, I mean, he is the billionaire and I'm just some schmuck. But I think his money is already going a great service for the world - ie it is staying in the hands of lots of corporations who employ lots and lots of people making products that lots and lots of people use and depend on. The capital in his corporations consistently grow, if you throw the money at a charity the capital essentially disappears after a one time use.