I can tell the difference, but I can't say I really prefer one over the other. So long as I'm watching a good movie, I couldn't care less if I can see the individual hairs on the guy sitting at a table in the background I will say that I don't think releasing older movies in Blu-Ray is always a good thing. I remember watching the beginning scene from Terminator 2 in Blu-Ray and realizing that everything looked super fake, because it was super clear.
Yes, as much as I love my HD movies, Porn is something that is best left at low res.