So much talent, data-mining has been spent on the problem of recommending what product you should also look at Amazon.com from the page you on, what Netflix film you should queue up next and what song you should listen to next according to the 512 acoustic attributes of the current one. Forgot all that, I want the next best clip to watch based on - one of the most frequently pursued and unacknowledged male (and female) activity on the Internet.
Data is all there. Tagging is categorized to the T on porntube sites by the actor/actress, genre, ethnicity and different acts depicted. Aggregator sites are already out there so all someone needs to do is build an aggregator site that plots out the user "interaction" graph from one clip to the next and make correlations. Next a snazzy Pandora interface where you could skip (unlimited times) to the next video, or show multiple preview of video's that you could skip to; or maybe make it social like turntable.fm where multiple people could vote to rock their socks off to a clip or not and see how long people in a particular room last... the possibilities are endless in pornification of the interwebz