Google’s PageRank and Inbound Links
Since its creation, Google has used a system for rating web pages known as the PageRank formula. This formula relies heavily upon inbound links to rank your site on a scale from 0 to 10, with a higher rank indicated a geometrically greater importance (i.e. a PageRank 6 site is about 10 times more important than a PageRank 5 site, etc.). The concept here is that, the more quality pages linking to your site, the more important it must be. PageRank from one page, then, builds PageRank on any page to which it links. The formula is actually much more complicated, but the concept remains relatively simple to this day.
Unfortunately, due to abuse by spammers, PageRank has lost some of its former value. Although Google’s not talking, it is clear that links from pages with PageRank below 4 are generally not even counted any longer in the algorithm. Because PageRank influences your site’s placement on Google, this means that any inbound links that you find should preferably come from pages with PageRank 4+, with a higher PageRank being many times more preferable.
The situation is complicated, however, by the fact that the amount of PageRank a page can contribute is divided by the number of outbound links it possesses. Thus, getting a link from a PageRank 8 page that happens to have dozens of other links will be of little use. In this case, getting a link from, say, a PageRank 5 site with a few links would be far more preferable.