I’ve been doing research on blogs and websites for years. I’ve seen websites that have no PageRank gain first page rankings and lots of traffic and sites that have PR3 or more that get no rankings and very little organic traffic. With this in mind, there is no evidence that suggests a higher PageRank will mean higher traffic, and in fact Google themselves even stated that site owners should not concentrate on PageRank but rather than building quality pages and content.
The use of PageRank is a Google invention and is not shared on other search engines. Since Google carries over 60% of the overall search market many people consider this number to a primary factor in the rankings of a website. Although this may seem true in some cases, as you can do searches and if you have a Google toolbar the PageRank is displayed, and may notice that some of the tops sites coming up have higher PageRank.
The problem with this is that its not true for all cases and people can quickly find many flaws in this theory from doing various searches. The reason it may seem like this is that the sites with better quality get ranked higher, and the PageRank is determined by the quality and authority of the page as seen by Google. This is why it may appear that PageRank is a factor in ranking, but in fact its a product of good planning, quality content, and authority within a space. In addition, these factors are also important in a site organic rankings and sites that have improved these factors may see an increase in both rankings and PageRank. For this reason, they may feel that they are working together, but in fact they are working simultaneous in conjunction with the same factors but are not effecting each other.