It's quite surprising how much effort has been put into developing search engine coding strategies over the years. Originally I used to think that it would be a relatively easy coding task.
But one easier approach may be to do what Google appears to do and monitor click through ratios and time spent on the landing page, assuming you can persuade webmasters to put your tracking code on their pages.
Terms such as collaborative filtering, sentiment analysis, and computational advertising seem very cool to me.
My forum signature is under construction.