Back to Buffett for a moment. What makes investors like Warren Buffett great is not just when they buy, but when they sell. Take Nalco, the chemical company based in Illinois. If you marginally know the name, it probably stems from the coverage of the Gulf oil spill. Nalco's chemical dispersant was widely used by BP as it frantically tried to deal with the problem. Berkshire Hathaway sold all of its 6 million shares in the last quarter.