Walrus- I would see no problem with installing a surface mounted box on the outside of the building for a receptacle or lighting fixture and supplying it with NM cable as long as you are just popping out of the building and entering the back of the box. I do see a problem with running conduit in a wet location and then pulling in NM cable.
This forum is an awesome location for these types of questions and I'm sure we will get some interesting comments on this subject.
