I have a problem making these working in a right way. When making any Serial.print af the analogs x or y of the gyro, i could realize that when i make a change on rotation of any of the gyro axis, lets suppose 30 degrees, and keeping it with that angle, i see an increment or decrement of the quid number but it always returns to zero. I have also tried associating it with the accelerometer according to Nuclear Projects :: INS - Inertial Navigation System, using the same program, and maybe tweaking it a little (since i dont use the same HW) but i always have the same result. It always returns to zero.
Big Assumption - I assume that by zero you mean the mid point, in my case its about 380 or 250 depending on what I am using for analogReference.
The gyro is supposed to return to the mid point, it reports the rate of change, not the amount of change.
When you stop after 30 degree of rotation, the rate of change returns to zero (represented by the mid point). During your rotation the gyro will be reporting the rate of rotation, move slowly and you will see a small change from the mid point, move fast and you will see a larger change from the mid value.