Msgraph at Search Engine Watch Forums does it again, he posted a thread named Google's look into document scoring by historical data. In that thread, he points to a patent issued by Google on December 31, 2003 on the topic of "Information retrieval based on historical data". The abstract reads; "A system identifies a document and obtains one or more types of history data associated with the document. The system may generate a score for the document based, at least in part, on the one or more types of history data."
Msgraph pulls out a quote:
 Consider the example of a document with an inception date of yesterday that is referenced by 10 back links. This document may be scored higher by search engine 125 than a document with an inception date of 10 years ago that is referenced by 100 back links because the rate of link growth for the former is relatively higher than the latter. While a spiky rate of growth in the number of back links may be a factor used by search engine 125 to score documents, it may also signal an attempt to spam search engine 125. Accordingly, in this situation, search engine 125 may actually lower the score of a document(s) to reduce the effect of spamming.
I still need to go through the whole document...