I've never really understood what people mean by 'identify with' in this sense. I don't imagine myself as one of the characters, or doing the things they're doing in porn scenes, but I do emotionally relate to what's going on with the characters - if I'm not emotionally relating to them, I tend to get bored and backclick. It definitely depends on the dynamic of the scene, though, because emotion-laden scenes make me think about the characters, whereas anonymous sex scenes (which are generally much less character driven) make me think more about bodies fucking & less about what's going on in their heads.

When I read other people's comments about how they do identify with the characters in porn, I always like though maybe I'm missing the point :-/