Each year the faithful make a pilgrimage to Omaha, Nebraska. Some 15,000 people descend on this unremarkable mid-western town, anxious to hear the wisdom of their humble guru. It is an event surrounded by ritual, adulation and a fair degree of cult worship. But this is not a religious sect, it is a shareholders' meeting. It's a billionaires' convention - probably the largest gathering of private wealth at any one time, anywhere in the world. Their guru, Warren Buffett, is an unassuming man in