Oprah Winfrey and Weight Watchers announced a partnership Monday in which Winfrey is buying a 10% stake in the company and taking a seat on its board. The company said it would broaden its focus to emphasize health and happiness, not just weight loss. Winfrey paid just under $7 a share -- about $43 million -- for her stake. Shares of Weight Watchers (WTW)more than doubled on the news, to nearly $14 a share. "Weight Watchers has given me the tools to begin to make the lasting shift that I and so many of us who are struggling with weight have longed for," said Winfrey. "I believe in the program so much I decided to invest in the company and partner in its evolution."