Tennis officials a-Twitter: US Open players warned - Yahoo! NewsNEW YORK – Watch what you tweet. That's the message tennis authorities are delivering as the U.S. Open gets set to start Monday, telling players and their entourages to be careful about what they post on the social networking site Twitter. Signs are being posted in the players' lounge, locker rooms and referee's office at the USTA Billie Jean King National Tennis Center with the header: "Important
