As you've likely noticed, search engines have become more and more dependent on metrics about an entire domain, rather than just an individual page. It's why you'll see new pages or those with very few links ranking highly, simply because they're on an important, trusted, well-linked-to domain. In the ranking factors survey, we called this "domain authority" and it accounted for the single largest chunk of the Google algorithm (in the aggregate of the voters' opinions). Domain authority is likely calculated off the domain link graph, which is unique from the web's page-based link graph (upon which Google's original PageRank algorithm is based). In the list below, some metrics influence only one of these, while others can affect both.