From a comment I made in a WF discussion.

Ord Allenbea's conclusion about quality content is dead-on. But the first statement about follow and nofollow is a fast-growing and erroneous statement. Per Google:

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All major sites like wikipedia, twitter, delicious, stumbleupon adds no follow attributes to external links. Adding no follow attribute to a link in your blog signlas google and other search engines to consider the site but not pass any PR to that. Another way to make best use of nofollow tags is adding nofollow to internal pages that do not have useful content in them to the visitos but still they are needed. Pages like "about us" "privacy policy" "contact us" are...

NoFollow and DoFollow. Links by their very nature are dofollow, meaning that a webmaster places a link on their site pointing to another site that they consider a relevant resource. This expression of relevancy has great value. Once this value was understood by webmasters, blog owners began to be and continue to be over-run by automated commenting bots released onto the net for the sole purposed of embedding links to be indexed by search engines knowing that these links would be counted as votes...