outland88 - 8:50 pm on Apr 26, 2012 (gmt 0)

it appears to me that most of them had their spammy links for quite some time --even for years--

Good eye, I'm definitely seeing that. Whether it’s a penalty I'm not quite sure of. Could be a combination of a Panda update revaluating a site, a loss of link boost, filters, and unnatural linking patterns. Plus some of this could have happened in the past few days or three weeks ago.

With the availability of PhD’s Google has probably developed a very sophisticated analogy as to what link spamming is and can analyze thousands of sites if not millions in a day. In fact it might be as easy as a comparison across genre’s and within genres. It’s the stuff PhD’s love to break down to a scientific level. They would take into account false positives but collateral damage would always exist. I wonder though if a lot of low quality small spam sites with few links and exact match domains might rank well because of this.

Great topic that I’ve been wondering about.