I remember the days when PR meant something. Back around the same time when I thought Betamax was the wave of the future.
Here is a nice article on PR calculation ... http://www.smashingmagazine.com/2007/06/05/google-pagerank-what-do-we-really-know-about-it/
PageRank is one of over 200 factors that Google uses to rank sites. I have a PR1 site that is outranking PR5 sites.