How would I fade out the edges of a plane, in Cycles? So, I have a render I am working on. It has an ocean plane, and then since I don't want really long render times, there is a regular plane that extends out to 10km. I want this plane to fade out to transparent near the end so I have a nice transition to the horizon (sky texture)

How would I set up the nodes so I can get the edges of the plane to gradually fade out?
You would just mix the main shader with a Transparent shader using a mix factor driven by a gradient texture. 



Here's a slight expanded version with an ocean plane and adding a Dif/Glos shader to the ocean surface before blending in the transparency.