Been studying up on how to create some render passes in Maya/Mental Ray. I'm using 2008 (so sue me), but this should mostly be applicable to 2009/10, as well, because there are some issues with the render passes coming out of both of those versions (mostly much longer renders, as Sagroth talks about HERE).
Basically the idea is to use the mia_x shader in particular to get a full spectrum of render passes basically at no cost (or little cost) to the render time of the images. This can be HUGE when you're rendering a longer animation or a series of animations.
Problem is that it's REALLY complicated, so I do it in three parts here. Part 1 talks about why you'd want to do this, Part 2 talks about the basic setup in Maya using the SimplePasses shader (which you can download HERE) and Part 3 talks about adding multiple shaders to your passes (both multiple mia_x and other custom passes) and some things to look out for re: render layers.
BTW, the script I'm using in the vids is here, though I make no promises about it. I fixed a couple things and can't replicate the weirdness from the 3rd vid, so I think . . . think . . . it should work OK for most things. To use it, source it, then type "zbw_renderPasses". If you open it in a text editor, there are some basic instructions in the header . . .
So anyways, here are the vids :)
Maya/Mental Ray: Custom Render Passes (Maya 2008) Part 1 from zeth willie on Vimeo.
Maya/Mental Ray: Custom Render Passes (Maya 2008) Part 2 from zeth willie on Vimeo.
Maya/Mental Ray: Custom Render Passes (Maya 2008) Part 3 from zeth willie on Vimeo.