Neal,

Great info!

Why does the zener noise decrease with an increase in current? I'm not familiar enough with this to know about it. I will give it a go when I wire it up on stripboard.

I like the idea of the temp compensation with a 'normal' diode in the reference string as well. (Which will help trim the voltage, as I'm using a string to get to the reference voltage...)

As for the ground, the idea of putting it straight to the load is quite sound. But where would that actually be on the motor board?