Just put this article together tonight...
http://www.mdvaden.com/tower_of_google.shtml
I've watched about 50 related websites that I could compete with for several years. Ones that I know the credentials of, and have watched the text and vocabulary of, down to minute details.
The conclusion is that Google's PageRank is dancing all over the place, up and down like a Yo Yo, while most of these sites have improved in content and quality, and 95% - wise, kept their solid upper results on the first page of search results for various keywords.
PageRank is fit for the trash can.