Mist in Cycles

I have this scene with a very long corridor basically stretching into infinity. But the render time is ridiculous because I added a huge amount of greebles. I could have set the camera so that it does not capture anything beyond a certain distance but that would look abrupt. Is there any way to create a mist effect at a certain distance like what you can do in Blender Internal?

Use the Z-pass to add it in the compositor.

Render with a Z-Pass, then use a Map Value Node (VECTOR->Map Value) and play with the values until the white is where you want the mist to be, then change the color and screen or add it onto the original.