Forum Moderators: open
About.com can be a killer source of highly targeted traffic, whether you get a free listing, use Sprinks or Advertise (or do all three) - although it depends on what topic you are trying to promote, since some Guidesites are far more popular than others.
About's users tend to be dedicated readers, coming back often for information approved by guides. In this sense, if you have a product or service a guide can give a favorable review to, that can be an enormous traffic generator.
Also, most of About's traffic comes through search on Yahoo, Google, MSN, & other engines - the different sites fair well in search rankings because of the quality & depth of their content, so someone looking for your product might come to an About site first, but then see your specific site.
hope that helps.
Then the guide site was shut down by About. :( Guess it didn't bring in enough advertising revenue... but I would imagine that a more popular About site could be a very worthy traffic generator.