CALIFORNIA: Ever since June 3 when John Mayer was pulled over in his rickety old Land Rover for not having a license plate, the Wonderland singer has been driving around town in Jennifer Aniston’s cars. “Obviously, she trusts him,” said a source. “She lets him drive her car even though his car is parked at her house.” Swapping cars isn’t the only commingling going on, obviously. Despite the fact that Mayer and Aniston haven’t been dating long, they already appear to have influenced each other or maybe even swapped personalities. “Before, she was kind of ghost, but now she is out a lot more,” a source said. “With her other relationships she has been a little more secretive, but this one she is not hiding.” As for Mayer, he has picked up a trademark Aniston trick of covering his face with a scarf in front of the paparazzi. “Jen used to do that all the time and he never did,” a source said. “She is clearly influencing him and vice versa.” No biggie. Start worrying about their Freaky Friday personality swap when she launches a singing career and he becomes an out-of-the-closet thespian.