After a discussion in this thread, I offered to share my implementation of the freaky details method described in the article of @patdavid. Maybe others could add their filters in this thread, too. I know that there was the idea once to share code in a repository but as far as I understand this was not really implemented or is regularly used. Also, I am not a developer and would prefer to keep things simple.
The Gimp filter below generates a new layer that produces the effect in combination with the original background layer. The advantage is that one can afterwards apply a blur locally to the sharpening layer. In this way one can limit the effect to certain regions. The script fu file has to be copied to the āscriptsā folder of Gimp and the filter can afterwards be found in the filter menu. The only thing to be set is the blur size.
I have to admit that I donāt code often and have no idea about Gimp scripts. So I just tried to gather information in manpages and examples and put something together. The script works quite fine when Gimp is freshly opened with a new file. However, when working with several open files, the script gets sometimes āconfusedā with the layer names. So, if someone can improve the code in any way I would certainly appreciate that 
. I used a gaussian blur in the script but you might want to replace this with other blur filters.
Freaky_Details.scm (3.1 KB) [This code is licened under the GPLv2]
Edit: The file was changed and now contains the adjustment proposed below by @Jade_NL.
