In June 2010, Bill and Melinda Gates and Warren Buffett started the GivingPledge: an initiative aimed at getting billionaires to pledge at least half of theirnet worth to charitable donations.So far, 40 individuals have signed up. Thelist includes household names like George Lucas, David Rockefeller, Larry Ellison,Michael Bloomberg and, not least, founders Gates and Buffett, who have pledgedsignificantly more than half of their net worth.