Carol Loomis, editor of Warren Buffet's annual letter to shareholders and a former Fortune writer says Buffett is driven by 'having fun' and not by making money. Loomis authored a book about Buffett called 'Tap Dancing to Work' and will be one of three journalists questioning Buffett during Saturday's Berkshire Hathaway (BRK.A, BRK.B) annual meeting, which she calls a unique event. Loomis says Buffett loves doing what he's doing, and that's what drives him to keep building his company. Loomis says Berkshire Hathaway is the fourth largest company in the U.S. and she expects it will keep betting bigger. While returns on Berkshire Hathaway's stock, as measured by book value, have trailed the S&P 500 over the past five years, Loomis says that's not an indication that Buffett has lost his touch and that book value is no longer the best way to gauge the company's performance. Loomis says for Buffett, running Berkshire has never been about the money. He's been driven by the idea of building a very significant company out of nothing when he took it over fifty years ago. Loomis doesn't expect Buffett to retire anytime soon, and says he keeps a rigorous schedule. Buffett, an avid bridge player, played with Loomis last night and she says they had 'a good game.' More than 40,000 people are expected to attend the annual Berkshire Hathaway meeting in Omaha, which would mark record attendance for shareholders who will also spend the weekend shopping and attending parties. Buffett calls this weekend 'the Woodstock for Capitalists.' Loomis spoke with TheStreet's Rhonda Schaffler in Omaha.