Ender, this is true, but speak to rev210 - he got some great times with 100kg of balast in the boot. On a dyno sometimes they put people in the boot. A serious drag car will try and loose as much weight as possible.
Try taking your car for a thrash with a full tank of petrol, 1/2 a tank and almost empty. I definatley notice a traction difference. In second with a near empty tank, from 30kph with 1/2 throttle and in a straight line my car goes sideways - doesnt happen with a full tank of petrol.
Remeber skylines dont have alot of weight on the back wheels for a drag car, which is why squat is so important on RWD for the drags, transfers to the back wheels.