IBM Stock: Warren Buffett's Investing Philosophy Tested By Berkshire Hathaway's Ongoing Stake In Big Blue

Warren Buffett isn't known for blown calls. But the billionaire investment guru and head of the holding company Berkshire Hathaway has become increasingly touchy around one of his top positions: International Business Machines. "We feel fine or we won't own it. We've never sold a share of IBM," Buffett told CNBC in an interview Monday. The fact that shares in the computing giant have fallen some 15 percent since he first started building his stake in the company in early 2011 hasn't phased him.