The porn biz seems to be a really good niche to go into as an affiliate marketer. It will always have demand and the competition looks very fierce, which is good as what most affiliate marketers will say. A very competitive market is the way it is because that is where the money is.
I did a little research on the PE niche and it seems that there is a chance to rank well in the SEs fo the long tail keys with decent amount of traffic a month. Probably worth a try to get an affiliate site up as there are a few clickbank products about PE. 
Jon