Comment on WordPress SEO Nofollow by SEO Dave.
Nofollow links pass no SEO benefit (they are SEO damaging to the page/site they are on), just trust me on this one I’ve tested it and at one point discovered an anomaly that the anchor text of a nofollow link was counted by Google on the page the link is on (not the case anymore, Google fixed it).
That’s not to say nofollow links to a site have no value at all, there’s click through traffic, but it won’t increase search engine rankings and it damages the site the link is on.
PR per se does not dictate rankings, but the number and quality of backlinks which can be roughly (very roughly) measured by the PR of a page is very important. Remember Google says they use over 200 ranking factors, PR/link benefit is just one Google ranking factor.
Looking at the PR of a page or domain alone isn’t very helpful, are the links that generated the PR aged, a link doesn’t pass full benefit for about a year, is the domain in a ‘trusted’ state which appears to be based a lot on the quality and PR of aged backlinks and if there’s anything wrong with the site (Black Hat SEO techniques). Are the backlinks spread over many domains or a few, are those domains ‘trusted’ sources. It’s not that hard to get a page to PR4 which can be enough to generate decent SERPs, but doesn’t mean the link benefit is working because of where the link benefit came from and how aged the links are.
In comparison the onpage SEO is easy and straightforward, but without those offsite factors you might as well not bother.