Now Maya 2009 can render output into multi-passes across the render layers. All is well But still it has few cons like Maya 2009 Multipass rendering cant support MentalRay shaders.
How Maya 2009 Multi-pass render engine works?
Mata 2009 Multi passes works with renderlayers and MentalRay renderer. With Maya shaders. We can render a scene in to multiple passes on the basis of which shading group we use. And it gives us great flexibility to tweak final look and feel in the post with any compositing software.
Rendering A Maya Scene into Multiple render Passes