===> See palms' description of the method below. The link to the original site no longer works.

Pity this link isnt working anymore as it is one of my favorites
but this is the gist of it

dup original >desaturate >duplicate
invert top layer
change top layer to colour dodge
gaussian blur ( so can see soft detail)
diffuse ( aniso )
new layer
use history brush to bring back some soft colour using a chalk brush ( or similar )
change blend mode to hard light


works nicely on furry animals ( not tried on buildings etc )
this was done quickly just to give a rough idea
photograph from www.geekphilosopher.com

Palms