I've read a few messages on here that start with "I'm an idiot,.."

So it's my turn,..

I'm an idiot.  For the focus distance guide to work properly, you must have the camera set to POINT AT the object you want to apply DOF.

The DOF guide lines will then appear with the correct orientation to the object your camera is aimed at.

I suppose, you could also do this dynamically, by having the camera POINT AT a primitive sphere.  Then the DOF would be oriented wherever the sphere is placed on the subject.  Just make sure the sphere is set to raytrace invisible before rendering.

BTW, I did notice that with extreme perspective, the preview camera is way off from the render.

Thanks for all your help everyone. :)

CG