Page Rank (PR) is a Google generated indicator, a number between 1 and 10, which shows how popular a webpage is; with 10 as extremely popular. Somehow PR's measure of popularity has been wrongly interpreted as an absolute measure for Search Engine Ranking Positions (SERPs). However a high PR will not necessarily equal a high SERPs for your keywords.
As has been discussed here earlier, SERP depends on relevance of a webpage to a particular search term or keyword. PR on the other hand depends on the number of links pointing to a page as well as the PR of those pages from where the links are coming from. However as opposed to SERP, PR does not take relevance into high consideration.
For example a website about mobile phone ring-tones can be featured by a site like Google.com. The link from Google is a PR10, a high PR that greatly contributes to the ring-tone website's PR. However, this same link contributes rather weakly in improving the websites SERP for the keyword "ring-tones".
In contrast if a site about mobile phones, lets say Wikpedia.com/mobile were to link to the same ring-tones website; the link would greatly contribute to the website SERP on the keyword "ring-tone". This is simply because Wikpedia's webpage is more relevant to the keyword ring-tones than Google's website. And what do you know; Wikpedia.com/mobile has a PR of 6 which is not a shabby. This then would mean the ring-tone website would get both a PR boost as well as a SERPs boost, making a link from a relevant high PR site more valuable than a link from just a high PR site.
So in a linking campaign it is wiser to chase links that also contribute to your SERP rather than those that only increase the PR. In doing so, take three things into consideration; first and probably most important is the anchor link text. These are the words used to link to your website. In the example above if Google were to use the keyword "ring-tones" in the text link it would contribute both to SERPs and PR. However if they use the name of website as is usually the case it would mainly contribute to PR.
Secondly, target high PR and highly relevant sites as discussed above. This allows you to have few links pointing to your site yet strongly impact your SERPs.
Thirdly, work to increase the number of links pointing to your site. Sheer number of links from somewhat related sites can add up to a boost in your SERPs too. This is especially a handy tactic if you cannot get relevant and high PR sites to link to you. All in all chase a better SERPs rather than a better PR; they have more implication to your bottom line.
