As you know, Google treats links from spammy sites vs unnatural links differently. But Google also treats different types of unnatural links differently as well. Unnatural links that are classified as “egregious link manipulation” would likely penalize a site whereas other links that are unnatural are likely just ignored by Google.

Gary Illyes from Google said this on Twitter:

Google’s new real time Penguin algorithm devalues links and no longer penalizes or demotes links – so this is a similar statement.

Forum discussion at Twitter