Depends on the porn. There's about a 75% chance I'll be all "OOH, I remember this!" and watch. If it's something REALLY nasty, like scat porn, I'll be all "wow, um, no." and walk away. If it's something really odd, like a lipstick fetish, I'll be all "huh... whatever." and walk away anyway.
As for ponies, it depends on the friend. A few of my buddies, I could see it happening. Others, I'd be all, "REALLY?" Either way, I think we would revel in pony goodness for 10 minutes, then go on with our lives.