Still waiting for the documentation to catch up with the product...
V-Ray can be a very involved renderer. It has a ton of features and the product gallery boasts some very impressive results.
However, the out-of-the-box usability really lacks. The setup is reasonable involved and although we've been able to get some nice preliminary renders, 3 different users were unable to duplicate the results shown in the tutorials. (Overall, the tutorials are poorly written and, subsequently, do not educate the user on what any of settings actually do.)
To add to our frustration, this plugin did not install a material library that is accessible from the in-rhino menus.
We were unable to locate on online documentation on how to bring in new materials or to build a material library.
Due to a lack of time to invest in using the tool, we've shelved it. Maybe when we get some time to talk to tech support or to figure things out ourselves, we'll give it a second shot.
The bottom line: We can see the value in having the tool, but we'll need to invest lots of time to figure out how to use it.