Marcia - 6:01 am on Apr 8, 2007 (gmt 0)

Naturally developed web graphs typically involve independent decisions. Synthetically generated web graphs, which are usually indicative of an intent to spam, are based on coordinated decisions, causing the profile of growth in anchor words/bigrams/phrases to likely be relatively spiky.

Exactly the point. Over a certain percentage of identical anchor text on inbound links cannot be done with independent decisions. Not 80-90% of the people linking will use the same exact wording of "money keywords" in the anchor of links, it has to be contrived. Natural development would be indicated by a certain amount of variation.

At the time the testing was done, there was a very specific figure - under nn% of indentical anchor text = no penalty. Having nn% or above identical = penalty. I remember the exact figures.

Changing anchor text of existing links is a different matter, and so is internal anchor text in global navigation and otherwise.