What I like to do (since I do a lot of my high res source art in ZBrush) is to utilize obj groups rather than materials to dictate how my mesh should be broken up within my rendering program. I'm not sure of a way to assign materials to polygroups in ZBrush, and the alternative would be taking my 4 million poly mesh into maya, selecting the faces assigned to the polygroups, and assigning a material. Which wouldn't be a big deal but a 4 million polygon mesh in maya isn't the friendliest thing to deal with.
Other render solutions have a few import options that allow the usage of obj groups rather than material assignments; you can discard groups entirely if you want, or you can choose to group by objects rather than materials. Since I can't seem to get material assignments out of ZBrush, this would be an ideal way to break up my source and assign materials that way.
Like I said, not a deal breaker really, and there might even be a script or plug-in that will do that conversion out there. Or Octane may do it I just don't know how.
