trying to compute the output data to be able to get the distance and speed from the acceleration... do motion capture
You're never going to get good enough samples to re-integrate velocity and absolute position from this kind of accelerometer. These things are extremely noisy and granular, and our sample time is limited by the i2c bus (Wii Nunchuck). Slightly better, get an ADXL330 without a Nunchuck so you're as fast as analogRead() but it still won't be very good.