A new plugin posted in the registry, quite interesting for line art and more technical uses
http://www.registry.gimp.org/node/25229#comment-11481

My use


experiments by PhotoComiX, on Flickr

or


experiments by PhotoComiX, on Flickr

From here


Rhys and me by dachalan, on Flickr

running the filter, blurring a bit,
on a duplicate of the same image repeat with slightly different setting

overlay the 2 new layers in overlay modeon top of the original
(multiply is nice to darken, overlay will do the contrary except for darker tones, the second image show a combination of multiply , for top layer and overlay for the other )

I just grabbed the filter a short time ago.I was waiting for a windows binary.
Nice results PC!

for the kind of use as in my example i believe is the main trick is apply on the detected edges a slight gaussian blur , from 1 to 3 px max.

i proposed for gmic so..cross the finger