| Bascially, coasting is not a recommended activity - if you're car is out of gear you're not in complete control of the vehicle as you're unable to accelerate should the need arise.
If travelling downhill, I would recommend selecting as higher gear as possible (if travelling over 40mph, use 5th or 6th) and apply very gentle intermittant throttle to maintain speed. The economy under these conditions is amazing, and you remain in control of your vehicle. | 
