Not in all situations. Depending on your car you may not have to worry about PS and Brakes at idle, my car does just fine while neutral idling. Like you said though it depends on the hill, a short little hill leave it in gear and coast. On long ones put it in neutral and glide. The reasoning is due to the engine braking created while coasting in gear negates the positive gain of no-fuel gliding. When you get back up to speed you may use more fuel than you saved gliding in gear. It all depends on the car and it's fuel demands. I can coast about 3-4x longer in neutral than I can in gear without losing as much speed, so it taxes less fuel over the whole distance even with picking up speed.

For flat land in gear coasting, let's say you can coast for 1/8 mile and then accelerate for 1/8 mile. If you were to maintain speed for the whole 1/4 mile it would cost you approx 1.7gph, hypothetically. If you glide you get 1/8 free, then you accelerate back up to speed at 2.4gph, so you average out to 1.2gph and save .5gph.

Same for neutral gliding. Coast for 1/4 mile at .2gph then accelerate for 1/8 mile at 2.4gph. You would spend 1.0gph at this rate assuming the same speed loss as above, I notice less speed loss due to the lack of engine braking so less acceleration would be needed.

Most people wouldn't do this simply due to constantly being on and off the accelerator, but in theory on a perfectly flat road with little wind it would yield results.

Clif's
regular = 1.7gph
in gear = 1.2gph
neutral = 1.0gph