I often tell my clients that blabbing about PageRank was the single biggest mistake Google ever made. PageRank was a brilliant concept, and Google was better by far than AltaVista, Excite, or any other competitor. But by revealing to the world how their search engine worked its magic, Google spawned the SEO industry - people who try to exploit their formula by means of exchanging links, submitting sites to directories, marketing articles, dofollow comment posting, xrumer, and so on and so forth. Instead of being smug and self-congratulatory, Google should have not ever filed any patents about PageRank, not talked to the media or anyone else about it, and kept the notion of PageRank a secret the way Coca-Cola and KFC have guarded their formulas. I bet that if Brin and Page could go back in time, they would advise themselves to not only keep PageRank a secret, but to spread red herrings, in order to further protect their secret. By red herrings, I mean misleading and completely false rumors like "the algorithm works by analyzing site owner profiles" or "it's actually based on font size". I wonder if a smart cookie like Aaron Wall would have come along and figured out the secret anyway. I'm not sure about that. Without the notion of PageRank in the public domain, the whole SEO industry wouldn't have come into existence, so guys like Aaron Wall would have pursued different career paths.
Uh...pagerank may as well be a secret. If it was truly understood, there would be a lot more sites with High PR out there.