With its trademark three-pronged star and celebrated German engineering, Mercedes-Benz has been the brand of choice for generations of celebrities, both actual and aspiring, from the late Pope John Paul II to Scarlett Johansson. It's a brand mystique most competitors can only dream about, and it has turned Mercedes, part of the DaimlerChrysler conglomerate, into an industry colossus with annual sales of more than 1 million cars and revenues exceeding $60 billion.
But these days the Mercedes star has dimmed. Just ask Lyn Murphy, an IT consultant in Newnan, Ga. She is shopping for a new car to replace her BMW...