1script - 7:38 pm on Apr 30, 2013 (gmt 0)
@jimbeetle: the seomoz article is rather nice and detailed but it takes one (hell of an) assumption and just runs with it. Unnatural links penalty is equated to receiving the unnatural link notice and is labeled "manual" without much evidence for it (anecdotal as always with G). I have observations and have seen people post theirs in the comments to the article that contradict that assumption.
1. I do have a site that received the notice and nothing at all happened to its traffic. Commenters to the post reported the same thing. It's hard to call it a penalty.
2. Unnatural Links notices have been issued en-masse just before Penguin, then started to come more random. Mass actions like this are not really compatible with manual anything. I see no mentioning anywhere that MC team worked overtime from early March to late April 2012
3. My own experience in moderating spam and low quality content of a large number of sites leads me to believe that true *manual* action in general has to be exceptionally rare. Simply because it does not scale well and Google needs everything they do to be scalable to the max.
So, I not convinced the issue is as settled as the author of the article makes it to be.