There is a technique the Hypermiling gurus call Forced Auto Stop (FAS) that involves taking the car out of gear - or even shutting the engine off - when coasting downhill.
One of the interesting things about my 2008 HOnda Accord is that the onboard computer does this automatically. WHen the car is coasting downhill, the throttle is closed, and the RPM is above idle, it automatically shuts off the fuel to the injectors.
Because the Accord shuts down 3 of its six cylinders when just driving along steady-state, I find that I get slightly better fuel economy by accelerating from a stop at a normal pace than if I accelerate at a very slow pace - it allows the engine to go into three-cylinder mode sooner.
