I was browsing around in Google's Webmaster Central yesterday, and I discovered that you can no longer view your 'live' PR distribution. You used to be able to find the live PR of your site in the 'Diagnostics' section under 'Crawl Stats', under the graphs of the crawl of your site.
This was often quite useful, as PR here is usually well ahead of the PR displayed in the Google toolbar, which is only updated every three months.
When asked about it, Google representatives said, "We've been telling people for a long time that they shouldn't focus on PageRank so much; ...We removed it because we felt it was silly to tell people not to think about it, but then to show them the data, implying that they should look at it."
From an overall perspective, they're right. Obsessing over PR isn't a very good idea. Yes, PR is still the most significant off-page factor in determining your SERPs, but obsessing over PR leads to neglecting other factors that are just as imortant but harder to quantify.
Relevance, and Uniqueness are two factors that are on the rise in terms of importance in search engine optimization. These are two factors that Google has specifically targeted in their latest update to try to improve result pages.
That's why it is more important than ever to check many different factors when selecting text advertisements to purchase. Yes, you still want your backlinks to be on pages with good PR, but that's not all you should look at. Make sure sites you select from our inventory are relevant, or related to your site. also, check that the page that would have your links is unique. Copyscape is a great way to check for uniqueness.
Although PR is still the biggest factor in SEO, Google is obviously takes measures to prevent it from being the ONLY factor.