It's certainly a tricky one. I've just found out about tangents and binormals which I'm still struggling to grasp but they are useful for building a somewhat stable surface based matrix..i think.
I'd like to do a bit of a write up on it soon, there's so many things I'm not too sure about.
For one thing, using MFnMesh.getClosestPointAndNormal() won't return a normal in world space if I'm getting the mesh data using inputValue.asMeshTransformed(). Is this a bug? Maybe I'm using it wrong.
Here's a quick demo.
