he world's third richest man has long been an investment "rock star." Now he's one on TV. In a new ad for Geico, a subsidiary of his company Berkshire Hathaway, Warren Buffett sports an Axl-Rose-esque kilt and croons, "We're always true to you."  Buffett has taken on a "tricky" challenge, but the ad works, says Daniel Gross in Newsweek, demonstrating that, while he takes his "responsibility to shareholders very seriously, he doesn't take himself too seriously." Other commentators are less impressed by Buffett's attempts to rock more than financial markets: "While there are doubtless some things moneymen and musicians have in common (hookers, blow, lunacy)," says Jessica Pressler in New York, "they're really very different." Watch for yourself: