Quote Originally Posted by niky
No wear and tear, but it's definitely safer to have the car in gear and engine braking while you're coasting downhill. I agree with sir ungas, better to be safe...

As long as the car is a modern EFI engine, it is using NO FUEL on a closed throttle as the injectors are not firing.
That's true, but unless the engine rpm is higher than a specified amount, say 1500 or 1800 rpm, the injectors will be firing (even with the throttle closed), just to keep engine operation smooth and consistent.

What you can do, though, is shut off the ignition while the car is coasting in gear. Just have to make sure to switch it back to the "on" position before the rpm drops too low.