I cannot reach the site from where I am now, but try to look at The Last Psychiatrist blog, it has an article right about that. Its main point is that there's a problem that cause both porn addiction and difficulties with sexual relationships, so that they're not directly related. I have to say that my experience agrees with that: I haven't any particular problem with my sexuality, and quitting porn for a couple of months did not had any noticeable positive or negative effect.