As many times as I’ve created a vignette with a mask, it only dawn on me today that the circle effect can also be used to create a circular vignette (and saved as a nifty preset.) Simply invert the circle, twirl open feather and soften the edges. This works well directly on a layer or on an adjustment layer.
Download a CS4 FFX file for the vignette here. Or look at the settings below.