Be sure to include solid materials (such as wood below - which automatically molds to the curved surfaces), and fractal plants - which create random, complex, detail without clogging the SketchUp model in the criteria for a good renderer.
(Just kidding of course - but it is an example of how a renderer comparison could be slanted to favor a particular rendering engine)
http://nxt.accurender.com/photos/examples/images/3753/original.aspx