Parameters

Sampling settings

Blur - The blurriness of the reflection. It defines how widely the reflection rays spread, in degrees.
(0 = perfect mirror, 90 = diffuse shading)
Samples - The number of samples used to calculate the reflection: the higher the blur value (the more the reflection rays diverge) the more samples you need to achieve smooth results, without unwanted noise. In general samples between 4 and 64 work for most cases. If blur is 0 than automatically only one sample is used.

Anisotropic sampling

Anisotropic Strength – Defines how strong the anisotropic effect will be: 0 is perfectly isotropic and a value of 1 makes the reflection blur only in the U direction. You must have exact mapping coordinates for this effect to work.
Anisotropic Angle – Rotates the direction of the anisotropic effect. When its 0 the reflection blurs in the U direction, at 90 it blurs in the V direction. There is no point of using values above 180, since the effect is symmetrical. (180=0, 200 = 20 …)
Normalize Angle for Texturing – Normalizes the Anisotropic Angle into the 0-1 range, instead of degrees. This makes texturing the parameter much easier.

 

Optimize Sampling

Blurred Raytrace Depth - Defines the reflection “depth” that still computes soft reflections. Usually you don't want to have soft reflections reflecting softly (that is raytrace depth 2) on another surface. :) Raising it over 1 can seriously kill rendering time.
Max Raytrace Distance - The maximum distance where raytrace calculations take place. If the reflection ray does not hit any objects while travelling to this distance it will automatically sample the environment image instead (if there is any). It can seriously speed up rendering and eliminate some sampling artifacts when used in big scenes.
Raytrace Distance Falloff – This value is added to the Maximum Distance and creates a soft transition between raytrace and environment reflections. It eliminates hard clipping of reflections on the objects.
(Max Distance and Falloff only works with Mental Ray 3.2 and above. That equals Maya 5 and above.)

Color settings

Color Gain - Modifies the reflection's color and intensity.
Saturation – De-saturates the reflection. (Most materials in real life doesn't reflect fully saturated.)

Fresnel - A switch that enables angle-based, physically plausible reflection values, based on Fresnel's equations.
Fresnel Strength - The intensity of the fresnel effect. (0 is like turning the fresnel effect off, 1 is fully fresnel based. This setting is not physically correct but makes slight modifications easier.
IOR - The index of refraction that is used to calculate the fresnel value.

Reflection bump

Enable Bump - If bump is enabled than the reflection can be mapped with a bump-like texture that effects only the reflections. It can be used to roughen up reflections or produce nice glass window-like distortions, without changing the base shader’s lighting.
Surface Bump - This is the channel that can be mapped with a texture, if reflection bump is enabled. (basically like Maya's Bump Value)
Surface Bump Height - This value scales the effect of the mapped texture. (like Maya's Bump Depth)