These contractions seem to add a lot of ambiguity though. Since "Backpfeifengesicht" is not commonly used, I thought it described a person who has been getting a lot of slaps across the neck so that his face took that form. Without context, these words are sometimes hard to understand unless they're commonly used.

Another example is Sitzpinkler. While this word is not ambiguous, it still sounds funny. I'd never use that and probably say "a person who pees while sitting". It might be used on some sign, although it makes the place where such a sign is found sound cheap because that word is really colloquial.

Nevertheless, it does create some great words such Schadenfreude, and Werdende. While i would never use Werdende, i believe it is used a lot in lyric (poems and that stuff). Schadensfreude is a really nice word through.

Disclaimer: my native language is German.