What’s more interesting about GoogleGuy’s comment is the reference to Google’s tracking of PageRank history.
A lot of sites that try to spam search engine indices get caught, and their PageRank goes lower and lower as their reputation suffers. We do a very good job of picking canonical urls for normal sites; sites with their PageRank going toward zero are more likely to have a different canonical url picked, though, and to a webmaster I understand that it can look like “hijacking” even though the base cause is usually your reputation declining.
There has been alot of speculation as to whether or not Google has implemented any result ranking based on historical data. GoogleGuy’s comment hints that Google is tracking PageRank history and determining results based on historical trends. In addition to using the current PageRank value, Google is considering reputation trends for web pages.
Most search engine optimizers felt Google was doing this. But I believe this is the one of the first public references from Google since the release of the patent.