I just launched
http://www.bestxxxporn.com and I must say everyone in this thread is right. It is a LOT of work, I mean a LOT. I knew it would be a lot of work going in though so I was prepared. I don't expect to push any kind of traffic before the end of the year. I have a ton of development left to do and I've got a Q of over 700 sites in the database that I need to review. I need to get a lot of that done before I even turn my attention to buying traffic, additional SEO, island feeder sites...
From signing up with sponsors to indexing all of their sites (and learning what passes come with what), to scoring sites, writing reviews, and doing all the design and development. It's a lot of work.
I expect in the end it will pay out or I wouldn't be doing it :P But like everyone has said. It's a major time investment and it won't be quick.