It's patent application time! Search Engine Roundtable points to a just published patent application (not an awarded patent) from Google (congrats to Matt Cutts who is listed as a co-inventor) that's titled: Information retrieval based on historical data.
From the abstract:
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.
Barry (aka RustyBrick) also points out that the app includes a brief discussion and definition of "link churn."
Link churn is "computed as a function of an extent to which one or more links provided by the document changes over time."
The patent application also notes that Google MAT penalize the web page owner for link churn above a certain threshold. Note the exact wording in claims 60-63.
Of course, this is just patent app that was filed in December 2003 and does not guarantee that Google is using, will use, or has used any of these techniques. Nevertheless, good discussion material.