The only thing I see in the 2008 manual that you can disable is the automatic pop up of the range indicator when the low fuel light comes on. I see nothing on disabling the lamp, nor have I heard of this prior to this thread. Could you maybe post the instructions that Smenard so those of us who might like to disable it could.
Personally, I like having it. And I will use the fuel gauge and warning light even though mine is off a bit. My countdown is accurate - sort of. When I fill it it shows 240 (approx.) to go. Pretty close. Then it stays there for 50 miles showing 240 to go. It might drop to 230 or 220 but usually not. Then it drops pretty accurately 1 mile down for 1 mile ridden. Then when it gets to 100 remaining it drops 2 for 1. So when it says 100 I got 50 to go. When it hits Lo I've gone 18 miles before getting fuel. I got 6.31 into the tank. That's right up to the neck. I only did this because of a closed gas station. I don't recommend it as a usual practice.
I would not trust the trip method. I usually like to stop when I hit that 100 remaining mark. Usually I get just under 5 gallons in it. I did it once after a long interstate ride west. I got 5.98! It appears I'd been fighting just a bit of a head wind and a bit of an uphill change in elev. Coming home I got almost 270 on the tank before it said 100 left and I only got 5.2 gallons in the tank.