I've had some featured listings with ExactSeek for a few months now. Based on the site's click reports, I thought I was getting a pretty good deal. However, I now use Google Analytics and I can see that incoming traffic from those ads has no value (1 page per visit and near 100% bounce rate). I now figure the only value of these listings is for the backlinks. The ad boxes are featured on many sites, the most important being GoArticles.com I think. The ads use a redirect link, but I know SEs still see that as a link to your site. Do backlinks from such ad boxes have good value? Or could SEs consider this spam since you suddenly get many links on new pages? (GoArticles.com publishes many new articles and a lot of them are very poor quality)
I got rid of all my ExactSeek listings and it didn't effect my SE rankings. I actually have better rankings than before but this is probably because of continuous SEO work and gradual increase in rankings. Bottom line for me, ExactSeek listings were not worth anything. If you purchase them, make sure to analyze your stats to see what they're really worth.