Operaguy, Yes the light will match the mapped background correctly. Bagginsbill has pointed out that one should reverse the U value in the image map (set to -1) for the environment sphere in order to match the IBL since we are inside the sphere & see the reverse of it. It seems to be correct.  He has uses his compass props to point this out, I will have to do a few test renders to triple check this with the most obvious examples possible. I will post something later today.  Got lots to do here in real world & burning daylight lol.... & I haven't even gotten to use my new mirror balls yet :-(. oh well one thing at a time