Google brought forward the idea of nofollow in order to discourage growing comment spamming in blogs and web. Google directed to put rel="no follow" in link tag wherever spam are expected, and soon other search engines joined this band wagon.
Because of fear of reduction of page rank juice, now webmasters are staying away from putting valid links at all. No follow has spread like aids virus and eating good content creators. There are many web sites whose sole content are aggregated from syndicated content like rss, xml, ipod streams. But the original content gets only no follow kiss. Some times there won't be a single valid link out of thousands of links from these sites. Presently spammers find innovative ways to spam with success , search engines sleep over their inability to find good content.