What is meant by 'now'? I'm sorry for my naivety!  What is 'now'?  How is it different from 'now' that was dt ago, or the 'now' that is dt in the future?  That is, what quality might the 'now' possess which the set of all other points does not?
If a point in space-time, then why is it that 'now' appears to a conscious mind to have the special quality of carrying the intense and unfolding moment of causality?
Is 'now' a special case of the set of all points in space-time to consciousness?
Is 'now' the moment of collapse of the wave function?  The moment of 'observation' or information passage?
Is it that 'now' can be described by different models (SR, QM, thermodynamics) and that I'm seeking the satisfaction of a anthropic 'now'; really a false question? 
Perhaps, I should admit the frame of the question and ask: what is it that, for a human being, gives the experience of life which is only ever contained in the fizzling 'nowness' of a point (or is it the (dt,dx,dy,dz)) in space-time?  Why does it appear to move, causally tracing a world line?
 A: I don't consider this a physics question, although it is an interesting one.

But what of my 'now', now? And your 'now' as you read this: 'now'? What's happening at these moments (S-T points) that is not happening there when the 'now' has gone elsewhere? Given no universal time, there is presumably no universal 'now'. All 'now's are relative. But even so, what bestows 'now'-ness to a moment?

From a physics standpoint, that is applying reductionism as far as possible, my opinion would be:
The events outside your brain are not considered in the now, as time has passed since your observations and they cannot be assumed not to have undergone changes since you observed them.
Inside your brain, where we might consider the most accurate  experience of  the now can be found, causality also applies. I have no idea what causes consciousness, but if we assume that a group of cells of some indeterminate minimum number will always be involved, there is still no absolute now, as it takes time for communication between these mininum number of cells.
So I would guess there is no absolute now, unless you believe that your consciousness arises from some other process, outside the realm of physics.
I think this question is a better fit for philosophySE, rather than any of the physical sciences sites.
A: As I put in my comments, "now" is more of a philosophical concept, especially when you want to think of it as special.
Given that "now" is as tricky of a word as you think it is, science typically strives to identify models in which "now" is not special -- any "now" is as good as any other "now."  If it can make the model independent of any specific "now," then it can sidestep the fact that "now" is poorly defined.
