A team from the University of Southern California is working on developing a low-cost parallel kinematic machine for multi-direction additive manufacturing. In this video you can see their 6-axis 3D Printer in action. Check it out to learn more about the printer:
6-axis 3D Printer From the University of Southern California





I suppose it would be useful if you are adding material to a non-flat surface. In which case a built-in scanner would be essential.
Agreed regarding the scanner for contour and topographic considerations. I think this is going to be a quite a big break-through: everything from increased structural integrity to multi-plane 3D-printed electronics. Would you happen to know of any similar projects WildZ?
actually there’s a student research in barcelona whoch is based on the same concept (additive manufacturing on different topographic conditions/freeform surfaces) check this:
http://www.iaac.net/students-research/open-thesis-fabrication-9/otf-2012-mataerial-petr-novikov-sa-a-joki-iaac-joris-laarman-studio-219
No, I can’t remember seeing anything similar, though I do remember seeing the article reference by bonooobong.
This technology would be very useful for any process where you wanted to layer different materials. As such, I see some variation of it becoming the next step in this fast moving technology.
I have already thought of a way to reduce the part count and cost of such a machine drastically.