Porn in fanfic can and does turn me on, but most of it doesn't (ie: the vast majority of porn battle entries do nothing for me). It totally depends on how the porn is written (I find more realistic sex much hotter than fantasy sex) and how the characters are handled (specifically, are they treated respectfully?). But I also find certain not-specifically-sexual H/C tropes turn me on, which I admit sometimes makes me think I'm a freak of nature. And, while only a subset of porny fic turns me on, I do sometimes seek it out for that purpose. Also, I'm more likely to be turned on quicker/easier by porn with women involved, but I also find m/m slash porn is much more likely to contain whatever it is that hits my buttons, which is frustrating.

As for telling the author? Heck no. I'll comment about the fic sometimes and occasionally about the sex scene, but I find it really awkwardly inappropriate to tell the author "your story sent me to my bunk" and I hate when I've gotten comments of that nature. TMI!