I've heard criticism that he's only doing it "for the publicity." My answer to that is "Who cares?" but this doesn't satisfy some people. As though you have to do the financial equivalent of self-flagellation to be sincerely altruistic.
EDIT for clarity: "Who cares" about why he's doing it, as long as he's doing it.
I've heard other criticisms that he is just going to give it to a charity fund in a similar manner to other billionaires who place their children at control of the charity and then use it as a way to pass on wealth to their kids without any taxation. Not entirely sure of the credibility of the claim that Mark is doing it, but I do know that this scheme has been tried and worked for others before.
Mark Zuckerberg annouced that he is going to give away 99% of his facebook wealth ($45 billion) over his lifetime.
He announced guiding questions:
It's interesting that "live much longer and healthier lives" is on the list. Larry Page seems to divert money inside Google into Calico for anti-aging tech. Under Cook Apple also invests into health.
The future seems looking good :)