It is about the rule book every Google quality raters get to use (shortly, people in charge of site browsing and evaluation). PDF document can be found here.
Variations of this document, like every item that contains are still valid to some degree (although this document is dated about a year ago). Considering that the document is pretty large (43 pages) I haven’t had the time to go through every item, but there are some people who have come up with interesting conclusions which can be read here and also a good review about previous and actual events related to the discussion here.
Considering all fact, it is a useful reading for webmasters and want to be sure that their actions are correct and valid according to the Google.
Aaron Wall gave his review on the topic, and one of his sentences confirms the double standards applied to the evaluation of content and page value.
In other words, spam is only spam if it does not help Google achieve its business objectives.
That’s how big fish do bussiness, isn’t it?