Since when has grease stopped people from buying fast food? And yes, their service is pretty good - I stop at Sonic all over the country and it's always the same: fairly quick, pleasant employees, food as expected. To me they have a bit more "personality" than McDs or BK.
Lousy service? Not where I live. I started following this stock after an experience I had last year. As I pulled in a girl immediately started walking to my car. She explained that lightning had taken out their intercoms. She took my order and relayed it to the kitchen with a walkie-talkie. As I waited for my food I watched 3-4 employees with walkies jog and skate to each car to take the orders. The kicker? They were smiling as they did it.