Saw a debate about this a month or two ago on a Jaguar forum, in among the tweed jacket buying guides and pipe tobacco reviews. The basic consensus was that yes, leaving the car in drive for ages and ages and ages and ages would ruin your torque convertor, but that most auto boxes are designed to be left in drive at the lights, and to move them out of drive into neutral every time you got to the lights would add as much wear and tear as not doing so. So it's six of one, half a dozen of the other really!