hi, i think pr is just one factor that takes part as you have to consider other factors too that are just as important & pr doesnt connet with SERP.
High PR is nice, but it is not the end goal of your site. There are better metrics to use evaluating when evaluating your sites performance. Targeted traffic, conversions, etc.
PR represents the popularity of your site and affects SERP but only as a part of many other factors including Quality Content that is the most important one...Good Content is still King!
©2008 Google — "Pages that we believe are important pages receive a higher PageRank and are more likely to appear at the top of the search results". (source: http://www.google.com/corporate/tech.html)