Would be cool to have a blend material with layer, to achieve the type of material below.
As you can see i have a metal base with hight roughness, then reflective paint material on top, and dirt material on top of the paint.
This give me the ability to combine material as the real life do.
I did it by using 3 planes objects with opacity, but as you can see, this would be so time/memory consuming by doing this on a whole project.
(http://postmyimage.com/img2/779_Blend_material.jpg)
We are looking into exposing this capability.
fantastic !