My apologies, I know I kind of dropped this after starting the thread, I haven't been back online until now.
I asked my friend about the whole sex scenes/nudity in movies vs. porn scenario, she said that it's more the intention that she objects to - the fact that when you watch a porn movie your intention is to masturbate or otherwise pleasure yourself and you will have an attraction to the person/persons onscreen whereas if it's a sex scene in a movie you're likely not watching that movie because of that particular scene, it's not part of the pleasure of watching it. I think for her it's more to do with the fact that if her partner were to spend their time watching porn, they are getting their sexual desires satisfied in a way that somehow involves someone else - the porn star in question.
I did ask her if she feels that masturbation is cheating since that's basically the same thing - you're fantasising about someone/something that isn't necessarily your partner, but she told me that was daft and it's not the same thing at all.
Personally I don't see anything wrong with it, as long as it's not taking over the relationship and the porn itself isn't something that has caused harm to the people involved. In fact until I had this conversation I thought everyone of my generation watched it to some degree! Turns out they don't.