Passengers tend to get upset when the engines stop. Pilots, too.

There are things that can reduce fuel consumption. For example, UPS is working with the FAA to test a GPS-based technology (ADS-B) at their cental hub. This technology reduces air traffic contol delays and saves fuel.

Higher precision navigation is being used in some areas (Washington DC, IIRC) to again reduce delays. Jet engines are very fuel thirsty at low altitudes so reducing delays can save a lot of fuel.

Airlines are really being squeezed on fuel costs so you should believe me when I say they're investigating all sorts of ways to safely reduce fuel consumption.