Coasting in neutral does not do you much good in fuel-injected car, because under the engine braking modern control units shut off fuel completely, whereas when coasting, engine is still running on idle. As for stopping at traffic lights, I usually switch to neutral to reduce wear of the clutch, and load on the engine. Better yet, if the stop is going to be reasonably long, I shut off engine completely, as restarting of a warm engine does not take much, while excessive idling is bad in general, and bad for fuel economy in more ways than one.