OMAHA, Neb. — While 81-year-old Warren Buffett's health has been on investors' minds, many shareholders at Berkshire Hathaway's annual meeting said Saturday that they aren't that worried about Buffett's prostate cancer diagnosis.More than 30,000 people are expected to fill Omaha's downtown arena and overflow rooms to hear Buffett and Berkshire Vice Chairman Charlie Munger answer questions for more than five hours.