Many blogging software packages automatically nofollow user comments, but those that don't can most likely be manually edited to do this. This advice also goes for other areas of your site that may involve user-generated content, such as guest books, forums, shout-boards, referrer listings, etc. If you're willing to vouch for links added by third parties (for example, if a commenter is trusted on your site), then there's no need to use nofollow on links; however, linking to sites that Google considers spammy can affect the reputation of your own site. The Webmaster Help Center has more tips on avoiding comment spam39, for example by using CAPTCHAs and turning on comment moderation.
Excellent post Brian. I think the point about writing content that appeals to influencers in spot on. Could you recommend some good, manual strategies through which I can spot influencers in boring niches *B2B* where influencers are not really talking much online? Is it a good idea to rely on newspaper articles to a feel for what a particular industry is talking about? Would love to hear your thoughts on that.