Is it me or do others find the screen calibration somewhat ineffective.

I find it especially obvious if you use lined or quadranted templates. The stylus does not line up anywhere close near the 4 corners. I have coloured the tip of my stylus to assist in seeing where it points & numerous calibrations make no difference. On a blank sheet it is possibly less noticeable.

I deal quite a bit at my job with those fancy expensive Cintiq tablets from Wacom. Same issue for quite a few of the artists to some extent:
- There will always be a layer (of glass) between the tip of the pen and the actual display tech, unlike the real world.
- The pen's sensor/emitter is not at the very tip but further up behind it. The tablet tries to guess where the tip -should- be (but on the other hand this helps to tilt recognition possible)

Practically speaking, when you calibrate, hold both the pen and the tablet in the position you would naturally scribble. Don't try to touch the calibration marks by getting unnaturally close and keeping the pen straight up (unless that's how you write/draw :)) After that, practice helps to get it to draw where you want.

My biggest gripe is the slow response time: to get something smooth you have to draw like you're underwater. I don't have high hopes this will be much improved, even if the vectorization is part of the problem...

The most important part of calibration is to hold the pen and DR exactly how you would when you write. If your hand/pen is at a different angle when you calibrate and write, the lines will be off.

Yes, I accept that and that compared my Wacom tablet it would be worse because the "screen" is thicker, what I am finding is that the "error" for want of a better word does change as you move across and down the screen.

A lot will be the way you move your hand and hence the stylus, it is just more difficult to be neat than I expected cf my wacom drawing tablet.