Good question, Ravensteve...one of your best threads yet.
But you know, money doesn't solve everything. It helps, but it's not the answer to EVERYONE'S problems.
Anyway - that's a lottttt of money to play with since he is among the richest men - (ever!) - but some of the things I would do is -
1) Donate, donate, donate. I don't have a lot - I live in a trailer in NYC and it's not very big when all five of us are home - but STILL - there are many, many, MANY people who are far needier than I. I'd start there, and ensure that everyone had a home, regardless of income. If it meant establishing many homeless shelters, then that's what I'd do - too many of us take for granted what we have and don't stop to think about how those who are less fortunate get by.
2) I would fully stock the above mentioned shelters with plenty of food and clothing for those who need them - as well as provide free medical care to those who don't have insurance or the funds to obtain coverage for themselves. Kind of hard to find medical professionals who would work for no pay, so of course, some money would go towards paying them - purely to ensure that those who can't afford to take care of themselves have no further excuses not to get the health care they deserve.
3) Schools - I'd make sure those schools had computers in every classroom, and that gourmet food was served in every cafeteria and that every student is entitled to a free lunch. No more of those long lunch lines and kids being hungry because their mom or dad isn't "eligible" for reduced lunch fees. Ridiculous, if you ask me. The school systems would no longer have any excuses to make budget cuts as far as education and nutrition.
4) Take care of my family and friends. Pay off debts. THEN, when all is righted and done, I would travel a little, take my family to see the places that we've always wanted to go but never had the money and time to do. Take my kids to Disney World, Universal Studios, Sea World, San Diego Zoo, go to Rome, Paris, Germany and Norway with my hubby...pay the babysitter very generously.
That's just some ideas off the top of my head.