Can the same effect of a graduated filter be applied through editing? Is there any advantage that using a GF filter would have that you cannot attain through editing?

Yeah, you can do it either by using a filter like the ones available from 55mm...

or by copying the image, superimpose it in the timeline and crop it (with a soft edge) - then add a color correction filter to the cropped clip and adjust the levels till it looks right...

or, easiest and best, by adding a black layer (created in Photoshop with a VERY soft edge) in your timeline and lining the soft line up to the horizon and dialing the opacity down... I've done all three in a pinch.. If the image moves, you do have to key moves for the matte..

BUT - it will NEVER look as good as getting it right in the camera.. and that is easy to do by buying a couple of filters... ND.6 & ND.9...

Jeremiah,

If the sky is overexposed, the only way to fix it may be with an ND grad filter on the camera. However, if everything is properly exposed, you can do it in-camera or in-post, no problem.

Josh