An interesting article in the New York Times a few months ago reveals some hints about how Google's parg ranking actually works. the article is available here: http://www.nytimes.com/2011/02/13/business/13search.html?_r=2&partner=rss&emc=rss
The article discusses how, over the last holiday season, Penney's came up number one in searches for everything from dresses to luggage to area rugs. The Times got an expert, Doug Pierce, of Blue Fountain Media to look into the mystery, and "what he found suggests that the digital age’s most mundane act, the Google search, often represents layer upon layer of intrigue. And the intrigue starts in the sprawling, subterranean world of “black hat” optimization, the dark art of raising the profile of a Web site with methods that Google considers tantamount to cheating."
Essentially, Penney's, or somebody acting for them, got thousands of unrelated websites -- mostly set up for exactly this purpose -- to link, via phrases like "casual dresses" to Penney's website. If you get enough of these trivial links, it really does raise your page rank.
A very interesting article about just how search ranking works, how Google works to prevent people gaming the system, and how occasionally, they miss.