I've signed up for a number of them. The best one was
http://hornyboy.com/
I would join more sites if I had time to enjoy them. If I were going to join a site right this instant to masturbate to it would be Ivana Fukalot.
I have no desire to sit around on free sites passing out stolen content even when I know that it's out there for the big sites. I want a membership, I want all of it, I want inside to see how it's presented. Even if I'm doing it for masturbation and not just research. I also have no desire to ask for webmaster access if I really just want to masturbate to the content or check it out for curiosity's sake; I just want to join it and enjoy it.