It's very easy to get to top 5 on "free porn". I've been developing couple of sites for a while based on this keyword. With investition of less than $1k you can get more than 100k uniques per day. I already have ready made landing pages for this kind of traffic that's been converting great with PPC, somewhere around 1:300! Imagine the number of sales with this amount of traffic!
Feel free to hit me up on icq if you are serious about this.