You are wrong. :) PageRank does not count for 20% of Google's algorithm. Yahoo doesn't use PageRank as it is exclusive to Google (although you can be sure they have something similar). PageRank used to account for a very large portion of Google's algorithm. In fact, it was what separated them from the rest and made the quality of their results so much better then the competition. But as we are very aware of now, PageRank by itself is not a good indicator of quality and can be easily manipulated. So, as time wore on, Google improved their ranking algorithm by adding many, many more quality indicators which reduced PageRank's value in their algorithm. While no one can say for sure just how much it influences rankings anymore, it is safe to say its role is greatly diminished and not very influential anymore. So much so that focusing on it is not a productive use of one's time.
Links from related web pages, especially those that rank well for the terms you wish to rank well for, are much more valuable then unrelated pages with high PageRank. PageRank is only an indicator of a page's link popularity, not its relevance for any particular search term. Since Google sees links as votes, a vote from a person who is knowledgeable on a topic is weighted much more heavily then a vote from someone who is popular but doesn't know anything about the topic.
This is why everyone who knows anything about SEO will tell you that content is king. Why? Because quality content will get you quality links. Quality links are those links from related websites that rank well for the phrases you want to rank well for. Webmasters only create those links when they see a web page that has the kind of content they want their readers to see. So, a smart webmaster will use their time to write great content instead of chasing PageRank. By doping that they'll get quality links and PR at the same time. Oh, and they'll get great rankings, too. All without having to ask other webmasters for links (or having to pay anybody for them, either).
