Is it a measure of anything that a developer or even manager can look at and get meaning from? I know at one time, it was all about the 7, 8, 9, and 10 PageRank. But is it still a valid measure of anything? If so, what can you learn from a PageRank?
Note that I'm assuming that you have other measurements that you can analyze.
PageRank is specific to Google and is a trademarked proprietary algorithm.
There are many variables in the formulas used by Google, but PageRank is primarily affected by the number of links pointing to the page, the number of internal links pointing to the page within the site and the number of pages in the site.
Thing you must consider is it's specific to a web page, not to a web site. So you need to optimize every pages.
Google sends Googlebot, its indexing robot, to spider your website, the bot is instructed not to crawl your site too deep unless it has a reasonable amount of PR (PageRank).