Hmm the idea of parallel cooling with smaller tubing may not be as stupid as it looks.
If you cool serial (the normal way, nb->sb->CPU for example) the last item will recieve warmer fluid than the rest. If you use parallel cooling they will all get the cool fluid, although a lot less.
The advantage of using smaller tubing is the fact that pressure will remain about equal. Going from 1/2" to 2*1/2" will drop both the fluid pressure and speed by quite a lot. Using for exampel 2*3/8" or 2*1/4" will keep the speed and pressure up a bit more.
But this is theory, I think the resistance of splitting and joining already makes this inefficient
If this is a single loop (can't even see that) I'm feeling sorry for the pump though :/
EDIT: oh and he should have left out the two (or even more?) temperature probes out if this is a permanent setup.