I've added some error messages about unsupported textures, a nonexistent scene "world", and a few other things. Unsupported textures are simply skipped now, with an error message in the console to let you know that it's unsupported and is being skipped.
The meshes that break rendering are usually reported by the Corona application itself, in the console. I've disabled the writing of edges to .obj files, since loose edges break rendering. I don't know if I've uploaded that change yet. At the moment, I cant even seem to get any geometry to break rendering at the moment. So maybe the new changes will at least help you in that regard :)
Occasionally I'll get an error about a mesh/material pairing, if I assign a material to a mesh, export the mesh, then change the material and try to render again without re-exporting the mesh. It gives a "Missing material" error. One way to fix this is to simply write EVERY material in the scene to the .mtl file, instead of only the ones that are being used by renderable objects. I'll go ahead and do that, so that it doesn't break rendering. The mesh will still need to be re-exported with the new material to give the expected results, though.