Well, I'm not into that sort of thing, but my mum wants to be. It's too bad she's an old bag and needs to start acting like one. She doesn't want to though. She still thinks she's "sexy and seventeen" and wants to do all sorts of (in my opinion) wierd crap like have "friends with benefits" and crap.
She asked my stepfather once (she was married to him) if he would mind having an open marriage. He said it was no problem, he was interested in other women. He lied. My mum screwed around with other people and he got severely pissed off. We were visiting in, well, the Netherlands (I wasn't born here) and he left us early claiming he was going to ship some stuff to us and ended up leaving us high and dry. He took all his crap and left the house, didn't pay any bills, essentially got us evicted and never spoke to us again. Let me mention he was the bread earner.
So, well, at least there is a testimonial to men that lie to make their partner feel like they're open and not actually meaning it.