I’ve seen people trying experiments in the node editor, just to reduce the noise of cycles renders. And such a way to reduce noise exists, and is integrated as a node: the Bilateral Blur node. What it does is a sort of selective blurring that doesn’t affect sharp transistions. But here is the nice part: you can use another image as an Determinator! This determinator image has to have sharp transitions in places where you don’t want your first image to be blurred. That’s why I use a mix of the Z and the Normal passes as my determinator.
To use it, you have to have 2 scenes with exactly the same geometry: one with Cycles and one with Blender Render (to render the Z and the normal passes). I use Add scene > Link Objects for that. Then you arrange the nodes like this (and you can play with the Color Sigma value):