You can see some response with credit-bases safelists, since other users have to open your e-mails in order to get credits and send out thier own. If you're promoting a product that's free, you may get some sign ups. So they can be a way to gradually build your own list that you can market to on your own terms. Also, they can be a way to get referrals signed up under you at other websites that would appeal to that crowd, like traffic exchanges, some of which pay you for referrals who upgrade to paid memberships. As far as making direct sales from sending out safelist e-mails though, I never had any success with it.