In May, Warren Buffett's Berkshire Hathaway filed a 13-F (a quarterly report disclosing a firm's holdings) that listed investments in what have been labeled "mystery stocks." Well, the wait is finally over, and the company revealed the mystery investments. Prepare yourself, it isn't exactly sexy: Berkshire Hathaway announced it took a combined $1.8 billion stake in homebuilders DR Horton and Lennar, and steel producer Nucor. Investor's Business Daily reports that Nucor traded up 6.2% to 153.34 before the open based on the news. Other notable investments included Berkshire Hathaway buying more than five million shares in UnitedHealth last quarter for a stake worth about $1.6 billion.