Matt Cutts has definitively answered this question.
We had to move fast when attacking spam. We attacked anything that looked like a content farm. But when most of the site is spam, there is nothing we can do. Even if you have some quality content but mostly negative content… nothing can be done.
He said that after Pubcon 2013 in defense of Google in a mini-argument with Jason Calacanis. The question then becomes how much is too much? My answer is ANY low quality content is too much since it's very likely that Google sees more of it than I do on my own sites.
- content created just to cover keywords
- pages where affiliate content is clearly the priority
- pages with too many ads, especially above the fold
- pages with little to no content (ie: empty profiles on forums)
- pages with content that is not very useful
- pages that rewrite, in your own words, what was already written about elsewhere(feels original to you, it's not)
- pages linked to by spam networks(including from your own sites if Google feels they are low quality)
- even if your site has the best content in the world and NO spam if can be labeled spam if you give it too many links from your "blog network" or other frowned upon linking practices.
Cleaning house and deleting or adding a noindex meta tag to these pages can positively impact the rest of your site, eventually(may take months or years).
Quick question: Do 100% of the pages attributed to you as an author have affiliate offers or advertising on them? Believe it or not most websites have no ads on them so that figure stands out.