I’m going to have to check out “Darktable,” a GNU-license photo management app similar to Lightroom and Aperture. It’s claim to fame (aside from being free) is it’s blazing fast performance thanks to GPU acceleration. If you like photography as much as me, and you are using a *nix OS, this is probably worth a look.
I’ve been playing around with a little app on my iPhone which creates NPR sketch effects from photos (I gather made by Bruce Gooch, who has done a lot to advance the state of the art in ‘painterly’ and ‘sketchy’ image manipulation.) ToonFX
The app is simple but with a little effort and insight you can get some good results.