A great Autodesk University class that converted me from Mental Ray to iRay for rendering. The talk by George Matos concentrates on how iRay is different from previous rendering technology and goes through the advantages and disadvantages. Later the talk moves on to cloud rendering with iRay and where it is all heading. Definitely worth a watch.
"Key Learning
Describe the hardware required for iray and explain how to use cloud rendering with iray
Explain what iray is
List the advantages and disadvantages of iray
Describe the differences between iray and previous rendering technology"
... Autodesk University