Recently ran into something similar - the preview showing black or in my case dark gray in
smooth shaded mode -,but didn't pay too much attention at first.Two days ago I had that
again and remembered this thread and started to investigate,because in my case it could
not be inverted
normals.My object had no normals at all.And that's what's causing the effect
apparently.Inverted normals don't.(see image)
I already knew ZBrush doesn't export normals (that's where my object was from),now it seems
that Cinema4d doesn't export normals,too,at least without that plugin.
Would be interesting to know what app Ulco had those problems with as he was the one
who mentioned the 'flipped' normals first in this thread.
You can see,if your object has normals or not by rendering it.Without normals it should
render as facetted,because the normal smoothing won't work.Another way would be to
look at the obj file in a text editor.
Sorry for being late.
Edit:The image shows how it is displayed in the preview window.