I'm getting my NEX's NPP set pretty well. I've almost got the buzz saw changed into a complete circle. But I noticed something about my camera and maybe about all NEX's.
If you use the grid lines on the LCD to center the camera on the South pole, you'll be way off. I had the center of the NN3 knob right in the center of the grid and the buzz saw test showed that I was nearly a cm off. After multiple test panos, I eventually moved the vertical arm from 5.2cm to 4.5 cm. Hard to believe the grid lines are that far off.
It might be that the camera bottom is not perfectly parallel with the optical axis. I don't know. Maybe there's something else happening that I haven't figured out yet.
The longer you do this the sooner you will realize that aiming the camera straight down is a good place to start, but due to manufacturing tolerances in both the camera and pano head (any pano head, any camera), you will come to realize that you are not done. Remember that cameras are not designed to do panoramas, so the manufacturer is under no obligation to mount the sensor in the exact same x/y/z position in the camera. Throw in the variances for lens manufacturing and you have a bunch of parts that were never designed to work together the way we want them to.
To get a better starting point, you aim the camera straight down, stand to one side, get down so that your eyes are level with the side of the lens and rotate the pano head all the way around. You will see the lens shift back and forth. Adjust the lower rail left/right until the lens does not move as you rotate the pano head through 360. If your camera is not mounted exactly square to the upper rail, you might not be able to dial out all of the lens movement.
You still need to do whatever calibration exercise works for you.
Although stitching software does wonders with rigs that are a bit off, starting out with a rig as closely calibrated to perfection cannot hurt but will only help.