I have a Lexus with in dash computer that shows miles per gallon.  I pop it in neutral every trip home from the mountain and get 70-80 mpg, when I normally average 20-21mpg.  All you have to do is watch the tach.  If the RPM's drop, you use less fuel.  Putting a car in neutral whether a stick or auto is going to drop the RPM's from 2-3 thousand RPM's to about 700 RPM's at 60-70 mph.  As for damage to the transmission, the torque converter is just like a clutch and slowly re-engages the drive train to the engine.  The only way you're going to do any damage is if you go past neutral into reverse.  Then you're in deep shit.  As for a carburetor drying out, it depends on what kind of fuel pump you have.  If it's a mechanical fuel pump, as long as the engine is turning, fuel is being pumped into the carburetor.  If the engine isn't turning, the fuel to the carb stops, however, you're also not using any fuel so the carb will not dry out.  If you have an electric fuel pump, which most cars now have, as long as the key is on, the fuel is pumping.  However, as several people already said, carburetors are few and far between anymore.  Most cars are fuel injected.  Just don't turn your engine off, as you will lose power steering, and worse yet, run the risk of locking your steering wheel.  There's no worse feeling that not being able to steer when you're going down a winding mountain road at 70mph with your steering locked straight ahead.  Oh, and also your power breaks will no longer work, so you can't stop either.  That would make for one very, very bad day.