The New York Times speaks to members of Google's search quality team - Udi Manber, Amit Singhal and one Mr Cutts - and uncovers some juicy facts about the state of the Google algorithm:
".. a far more elaborate system for ranking pages, which involves more than 200 types of information, or what Google calls “signals.” PageRank is but one signal. Some signals are on Web pages — like words, links, images and so on. Some are drawn from the history of how pages have changed over time. Some signals are data patterns uncovered in the trillions of searches that Google has handled over the years."
including QDF (Query Deserves Freshness):
"a mathematical model that tries to determine when users want new information and when they don't."