David Hackett with a post looking at Unified sampling in Mental Ray by way of the Elemental Ray Blog. unified sampling is a sampling algorithm for Mental Ray which has a bit of intelligence to it compared to the brute method of Anti-Aliasing sampling. Check out the post for A Simplified Look at Mental Ray Unified Sampling here.
David Hackett writes: As a simplified look at using Unified Sampling as a more “brute force” method that was outlined here; the below example outlines the differences in time and sampling on a visually trivial scene. This should make some things very easy to understand and quick to read before moving on to lights.