I watched with my ex-girlfriend. It was actually always she that wanted to watch together, otherwise I watched only when she was away, not like I was keeping it a secret or anything, 'cuz she probably watched as much as me!
Although I never really told her the full truth about all the stuff I watched when she asked. If she knew about all the gangbang/bukkake and that stuff I guess she'd be pissed. We watched girl-girl 9/10 times, and the 1/10-time, it was home made amature couple-stuff.
Now I'm dating a new girl, and she told me just the other day that she's into porn, which came as a big relief, because she have given me the impression she was the pretty anti-porn-kind of girl kind. But it didn't stop there... She told me she even considered doing porn as well!
Not gonna happen on my watch though...