Just a sampling from my personal experience:

1) fucked my neighbor's sister up against the side of their house while her husband was passed out
2) girl I went to school with, her husband of 3 months fucked her distraught just-dumped friend on the couch while she was sleeping so she left him.  I offered her a sympathetic ear and a hard cock; it felt good to help someone out and I think I made a difference.
3) fucked my first female boss on her desk, in my car, in the bathroom, in her hotel room at a conference, on a running trail (to name just a few), and on a conference table in my office a year later when I was at a different company.  Went on over the course of 3 years and she had the same boyfriend the whole time.
4) fucked an ex in the water at the beach while her date hung on to my wallet, keys and pager (yeah it was awhile ago) while we "went for a swim."
5) another friend banged his next door neighbor every night for a month while her husband was off in training somewhere and she was home caring for their toddler

Those are the tame stories, I've got way worse (better?) ones.  I'm convinced that most of those that don't fuck around lack either opportunity, nerve, or are just resigned to live a bland existence...but I know they dream of getting wild.  I've seen one too many middle aged men have a few too many and start the "that bitch I'm married to" speech not to believe that.  But I also believe maybe one in a thousand couples get hot and stay hot for each other ...and I think it's the ones that post reviews of the provider they saw together.