Oops! Its actually a Maya node and not a Menta Ray node but it works with both renderers. The easiest way to use it is when you want to create a rim of light on a particular piece of geometry ... but it really is capable of SO MUCH more! Try this ...

In HYPERSHADE create a ramp. Now drag and drop the SAMPLER INFO node on top of it and choose OTHER when picking a connection. This will bring up the CONNECTION EDITOR. On OUTPUTS choose FACING RATIO. On INPUTS choose U COORD. Now set the ramp to a U RAMP under its attributes. Now just drop that ramp onto a lambert (or whatever) and plug in into ambient color and plop it onto your geometry. Adjust the ramp colors to taste.