Taken from http://www.digg.com/design/How_A_Scanner_Darkly_Was_Done

Artistic>Poster Edges Filter (10,1,6) but adjust accordingly
Noise>Dust and Scratches (1,1)
Stylize>Diffuse (anisotropic)
Artistic>Film Grain (2,16,10) adjust accordingly

Optional to create "banding effect"

Artistic>Cutout (8,0,3) adjust accordingly
Edit>Fade Cutout (65%) adjust accordingly