QUOTE: “An infinite number of niches are waiting for someone to claim them. I’d ask yourself where you want to be, and see if you can find a path from a tiny specific niche to a slightly bigger niche and so on, all the way to your desired goal. Sometimes it’s easier to take a series of smaller steps instead of jumping to your final goal in one leap.” Matt Cutts, Google 2006
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 spam40, for example by using CAPTCHAs and turning on comment moderation.