For the last 2004, Google was updating their index and they were trying to clash simulated links with this update. Google developers and people under its institution pointed out that Google was trying the better ways to verify the importance of website links.

The problem of Google during that time is that many people don't link to related pages. What's important to them is to link and link their site to the other sites with higher Page Rank (PR). But they only accept links from the site with high PR. Google identified the problem and possibly show the garbage backlinks and it may not update the PR. To solve that problem, it manually penalizes sites for buying or selling PR links. But now, Google is different, they have automated system software to penalize websites violating their rule.  

In fact, it is not important of having a high PR or gets many links from unrelated website as much as possible. The important thing to consider here is to get links from website relevant to yours even  if that site has low PR, but having a low PR is not a big issue because later that website will soon earn higher PR, while still linking back to your site. If you are on link campaign and found a website with a great posts but low PR, then you should trade links with it regardless of its PR.

As a link builder I have a simple trick on how to find my right link partner. First, go to http://www.seochat.com/ and on the left side of the page under SEO tools there is a tool about Page Rank Search, click it, and in the text box, type your keyword, as for example: "IT outsourcing", it will show the result according to PR and look for the website having the good content and ask for link exchange. But if you want another SEO tools for searching website with higher PR, just go to Google.com and type the keyword: "Page Rank search", observe if the result is consistent. Then, it's up to you how Google is better than the other search engine.