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.
A generation ago, consumers were at the mercy of advertisers who spoon-fed them marketing messages across a few media channels: print, billboards, television, radio. These advertisers created markets, defining and reinforcing consumer stereotypes. In the 1950s, advertising was primarily a one-way conversation with a captive audience. TV advertising grew and matured into a viable marketing medium. Experts were the style makers.