idle, or switch off?

Adam Kotsko has a question that has often crossed what passes for our mind:

In general, is turning off one's car rather than idling, for instance at a long stop light, an effective way to save gasoline? Does restarting the car take such a significant amount of gas that the wait would have to be unrealistically long to produce a net savings of gasoline?

Go read the comments to that post. And do come tell us if you have a different opinion. (: Adapted for Indian road conditions, of course. :)