NoFollow is an HTML attribute (rel="nofollow") that was created so that site owners can tell the search engines to not pass on PR value to any links with this attribute during indexing. These days, most blog platforms are installed with the default setting for NoFollow enabled. For those who comment on blog articles, this means that the URL in the comments are spidered, but are not given any PR value by Google and other search engines. Many SEO's have argued that a nofollow attribute negatively impacts the URL it links to. This is patently false, were it true, it would be all too easy for unscrupulous marketers to spam their competitors links to thousands of blogs using the nofollow attribute. A nofollow link does not harm your site, but it doesn't benefit it either.