Owen Wilson and Jennifer Aniston have become fixtures in Miami, but it's not all fun in the sun. They're in town shooting their romantic comedy Marley & Me, based on the nonfiction bestseller about a family and their beloved dog. When she's not reading scripts while sunbathing, Aniston, 39, spends her time sipping lychee martinis at the Mandarin Oriental Hotel, shopping at Prada and enjoying dinners with girlfriends at the Blue Door at the Delano. "She seems very at home," says a set source. Wilson, 39, is also keeping a busy social calendar. At the Shore Club Penthouse March 7, he recited Wedding Crashers lines with a reveller while sipping bottled water. "He seemed really content," says a partygoer, "just chilling out in Miami Beach."