Observers of Warren Buffett's Berkshire Hathaway have grown used to a drumbeat of filings saying the company had sold shares of Bank of America. Trades made public late Thursday brought Berkshire's stake in Bank of America below the 10% threshold that triggers a requirement for frequent reporting. After the newly disclosed sales, the Omaha, Neb., company owns exactly 775 million Bank of America shares—a nice, round number that corresponds to 9.99% of the bank's outstanding shares, according to Dow Jones Market Data.