Well, Steve Ballmer certainly had a productive week. Over the past three days, the Microsoft CEO has sold 49.3 million shares of his company stock, Reuters reports. With the share price hovering around $27, the sale has made him about $1.3 billion. Not bad for three days. And he's not done yet. Ballmer apparently intends to sell as much as 75 million of his shares in total by the end of the year. At the current prices, that would earn him about $2 billion, all told.