Twitter takes on Facebook: Let the social rumble begin

It seems Twitter has put on its big-boy pants and decided to take Facebook head on. In an appearance on NBC's "Today" show, Twitter CEO Dick Costolo introduced several major changes to Twitter's website and mobile apps. For example, the network now lets you upload a large "header" photo to your profile page, making it look very much like Facebook's new Timeline.George Lopez Regis Philbin Serena Williams Ryan Seacrest