smallcompany - 12:37 am on Jun 8, 2012 (gmt 0)

I'm starting to think that small scale sitewide links in the footer for example are just devalued or ignored but there is a threshold or a ratio that leads to something more dramatic.

Sounds reasonable.

That's why Penguin to some websites could be like a plain wasp trying to bite an elephant while to some other is like the same wasp biting on a tiny fly and eating it up.
Same thing having way different effect depending on the total backlink portfolio quality (however G sees it).