Where can I find some info on thin film iridescence as it relates to Brazil?

Post Fog and DOF appear to be unavailable?

The thumbnail for a given material looks generic and does not seem to represent changes made while editing in the materials panel. What gives?

Iridescense is a feature we threw into a service release - sorry, we didn’t add the docs for it. I will put something together a little more this week. However:

Iridescense simulates the refraction interferences that happens when there is a thin film of a substance covering the main surface. Usually this film is some kind of oil - and the result is a split spectrum of color which is view dependant. The basic parameters are the IOR of the film (which will differ from the main material) and the thickness of the material. Since the thickness can change over the surface, there are also minimum and maximum values along with the texture slot to vary the value.

The default values should already give you interesting effects.

Post effects are dependant on the Frame buffer channels - which are off by default. You will need z-buffer on for those two.

The material thumbnail certainly updates here. Do you have a specific example?