Nem, is right. You can get get great results just starting with 3-point lighting and going from there. The render time is much quicker. The problem is, people see some great renders and hear that the person used GI_Joe then all of a sudden think it's going to be the end all solution to make beautiful renders so they have to have to check it out. I did the same thing.

One thing that makes me curious is if you have mentalray for maya, why do you need GI_Joe? GI_Joe is a script to compute pseudo global illumination. Mentalray with Final Gather is the real deal. Render times can be a little long depending on the amount of rays used but the results can be worthwhile. You might want to look at these tutorials:

Global Illumination in Maya (with MentalRaya 1.5)

Caustics and surface scattering with mentalrayFinal Gathering in Mentalray

Mentalray - Faking HDRI

Caustics in Mentalray for Maya

Various mentalray tutorials