Faizal Taher takes a look at Unified Sampling in Maya Mental Ray and explains a bit about what Unified Sampling is, and how to implement it in Mental Ray for Maya, using the string options to add the Unified Sampling options to the Maya interface (in Maya 2012).

the process of setting up unified sampling in Maya

Faizal notes that using the Unified Sampler in Mental Ray is similar to the DMC Sampler in V-Ray in that you are able to change sampling parameters in one handy area, noting a couple of minor differences as he goes. The ElementalRay blog has some great information on Unified Sampling in Mental Ray, particularly the Primer with settings comparison renders that you might want to check out here.