There is an interesting thread going on at Outfront on the subject of Page Rank. Specifically, what goes into calculating not only rank, but how rank should be looked at as only part of the equation in determining how a site is treated by Google and some of the other engines. Here is an excerpt from one post in the thread:
... you have on-page optimization factors and off-page optimization factors. Both are important, but IMO - off page/off site factors are more important.
Here are a few on page factors: meta keywords, meta description, keywords in title, domain name, position terms in title, page size, (h1, h2, h3, h4), words at the beginning of sentence or paragraph, valid HTML, text to html ratio, anchor text, alt text, broken links, internal linking, proximity of keywords to other factors, keyword density in body, bold/italic/other keywords, file name, file size, text around links, age of site, age of links, case of keywords, misspelling, bad grammar, plurals and many many more.
Off page: Page rank, anchor text (and all that goes with it), theme of site linking to you, number of back links, server response time, SEO programs, speed that links are required... basically links, links, links.
As you can see, the complexity of what goes into determining how your sites fares goes way beyond one or two factors.