A ton of spam. While the right sponsor obviously is important, maybe all will convert bad for your site?? I know I have many sponsors that convert for shit most of the time. I think Jesus hit the nail on the cross. Some keywords, like traffic to theHun serve those mostly looking for free porn. Before all the hate posts come, TheHun is great site and if you have a zillion visitors, you can live with 1:12,000.
My
If you think your SE traffic is the free porn type, maybe promote something else besides what you are already showing them for free. Dating, pills, sexguides and webcam come to mind.
Of course you'll find those things listed in my sponsor list too.