Billionaire Warren Buffett remains optimistic about the U.S. economy, but he says it's difficult to predict when the recession will end because American consumers changed their behavior significantly. Berkshire Hathaway's chairman and chief executive conducted several TV interviews Monday after entertaining 35,000 people at his company's shareholders meeting in Omaha over the weekend. "In the short term, things are going to be tough for a while. We see no real pickup in a whole variety of businesses we have, but they'll be doing fine in a few years," Buffett said Monday in an interview with CNBC. Among Berkshire's more than 60 subsidiaries, there are furniture, brick, manufactured home, carpet, utility, insurance and jewelry companies, so Buffett gets a good sense of the health of the economy by looking at his internal reports.