Thanks Matt for the informative post. However I do have some questions regarding blog comments. Let say a blog post of mine have PR 10, the page has 10 links, 3 of them are my internal link to my other related post, the other 7 links are external links from blog comment. Based on your explanation, even the 7 external links are nofollow, my 3 internal link will only get 1 PR each which is still the same if the 7 external link is dofollow. Therefore there is no point of adding nofollow for the sake of keeping the PR flow within your own links. Is this correct?
While ordinary users were not that interested in pages' scores, SEOs of a different caliber felt that this was a great opportunity to make a difference for their customers. This obsession of SEOs with PageRank made everyone feel that this ranking signal is more or less the only important one. In spite of the fact that pages with a lower PR score can beat those with a higher score! What did we receive then, as a result?