Referencing in Maya is great in theory but there are a lot of bugs in practice. The scene needs to be set up in a certain way to ensure that the referencing works properly. This can be done by hand of course but can get tedious. Here are some useful bits of python code that can be used to speed up the process.
This is some code I wrote a while ago to semi-automatically convert Mental Ray materials to VRay materials. It should work for the most part but, of course, some of the attributes don’t have exact equivalents.