We were sitting in a Manhattan living room on a spring afternoon, and Warren Buffett had a Cherry Coke in his hand as usual. But this unremarkable scene was about to take a surprising turn.

"Brace yourself," Buffett warned with a grin. He then described a momentous change in his thinking. Within months, he said, he would begin to give away his Berkshire Hathaway fortune, then and now worth well over $40 billion.

This news was indeed stunning. Buffett, 75, has for decades said his wealth would go to philanthropy but has just as steadily indicated the handoff would be made at his death. Now he was revising the timetable.

Buffett has pledged to gradually give 85% of his Berkshire stock to five foundations. A dominant five-sixths of the shares will go to the world's largest philanthropic organization, the $30 billion Bill & Melinda Gates Foundation, whose principals are close friends of Buffett's (a connection that began in 1991, when a mutual friend introduced Buffett and Bill Gates).