I am not sure if the subject heading is appropriately un-ugly enough; there is more than enough out there on the subject of m4.
Here are a few border-line awesome uses of m4:
http://www.seindal.dk/rene/gnu/m4lib/
http://uszla.me.uk/space/essays/m4Y
http://209.85.173.101/translate_c?hl=en&sl=ja&u=http://ya.maya.st/d/200703a.html&prev=/search%3Fq%3Dcurry%2Bm4%2BAND%2B%2522(*)define%2522%26start%3D20%26hl%3Den%26rlz%3D1G1GGLQ_ENUS241%26sa%3DN&usg=ALkJrhjp32n1_vh_FSwBXHu_DiAmJsrAVg#d20070306
www.cs.stir.ac.uk/~kjt/research/pdf/expl-m4.pdf
Particularly interesting is the possible use of macro expansion in the production of new uses, like y-combinator, curry. concatenating arguments with indir,..
Please share with the community links to readings, projects on the topic of meta-programming using m4.