I debated whether or not to leave this question open. I am going to on one condition: PLEASE stay appropriate. There is no reason that we cannot have an adult discussion of this nature without it turning into something bad. NO LINKS to your stash will be allowed. No telling each other where to find it. Nothing of the sort.... please. :)
My first reaction was to flip out at the thought. I have a fifteen year old daughter. And then... I stepped back and really thought about it. She is curious, much as I was at that age. Much as ANYONE is. There is nothing wrong with watching porn in and of itself. Would I ground her? Nah. Would I sit down and talk to her? Yup. I wouldn't yell at her for it, but I would caution her as to the safety of it, answer any questions she had, and the like.
That doesn't mean I'd be happy about it, nor that I condone it. However, teenagers are going to do things we don't like. It's a fact of life. We cannot put them in a bubble and only allow them to do what we want. There comes a point we have to let go as parents and trust we raised them right. :)