Hard to know, but anecdotal evidence from insiders is that it's akin to printing money. Don't ask, don't tell It's no surprise that Web portals don't break out revenues derived from porn advertising. That sort of news does not make for the kind of PR they like to trumpet. But don't expect them to go cold turkey anytime soon. It's the unspoken truth of portal sites.
Click rates are typically higher than on banner ads.
Advertisers pay because it's all performance-based and this stuff translates into big sales. I wouldn't hammer the portal guys too hard . You find the same predictable hypocrisy practiced by cable companies, which carry porno through their pipes but don't talk about it. My philosophy is live and let live. After all, anyone over 21 should be able to view whatever they want on the Internet.