After being asked several times for the Maya 2008 version here it is - pretty much in time for Maya 2009 ;)

This shader is almost the same as the Mental Ray Ambient-Occlusion-Shader but for the default Maya Renderer.

Version 1.4

* Added Maya 2008 32/64 bit support

Version 1.3

* Added Maya 8.5 support

Version 1.2

* Added Maya 7.0 support

* Added a "Add Bounced"-Checker for easier in-node compositing of the original and the bounced color

Version 1.1

* Added Fake-Final-Gathering which takes the occlusion-rays and samples the color of the collided geometry. This results in a color-bleeding effect which looks kind-of FG.

installation:

-copy "ds_ao4maya.mll" to your "../Alias/Maya8.0/bin/plug-ins"-folder
-copy "render_ambientOcclusion.xpm" to your "../maya/VERSION/prefs/icons"-folder
-restart maya
-load the ds_ao4maya.mll (Window -> Settings/Preferences -> Plug-in Manager)
-you'll find the Ambient Occlusion Node in your Hypershade (under Surface)

info:

while looking at a tutorial for programming shaders for maya i was wondering how complicate it would be to create an ambient occlusion shader for maya. it wasn't too hard ...

attention:

you should be aware that this node definitly won't be faster than the mental-ray one if you want to achieve production-quality. The fg-fake mode
is very slow and originally just a possibility-test.

usage:

-don't forget to switch on raytracing

-everything works almost the same as the well-known mr-node

Fake FG usage:

-the shader computes the occlusion-rays and asks the collided geometry which color they have. Combining these results in a color-bleeding effect which looks kind-of FG.
-if the shader itself is asked for it's color (ray-depth > 0) it returns the color of it's "Bright"-attribute.
-so if you want to achieve a result like the third picture in the attached image you have to connect your original shaders (different colored lamberts in this case) to the "Bright"-attribute of new created ao4maya-nodes.
-have a look at the supplemented maya-scene!
-if you're using raytraced shadows don't forget to set their raydepth limit two at least 2

if you discover any problems / bugs please tell me!
if you achieve a nice rendering with it i'd be excited to see it!