Many of them are middle-class, many have young children.
"I want a man with a personality and looks to take my breath away." These are the requirements of the dark-haired, dark-eyed, 37-year-old Asian beauty who has sent me her romantic wish list.
Reading it on my laptop in the aptly named Cafe Affaire in central London, I consider what she really wants: a no-strings-attached sexual relationship.
What I don't know is how her husband will feel about it. Aside from the little matter of her marital status, she also believes I have a wife, but she doesn't care.
She wants instant gratification even though we've exchanged only a few words online.
But in the modern world, in which the internet has become a vehicle for all manner of impropriety, she regards this kind of behaviour as perfectly acceptable.
We have encountered one another via an internet dating service established for the sole purpose of enabling married people to commit adultery.
It may sound like an unpleasant niche website for a handful of amoral people to whom wedding vows never meant very much.
But it claims to have more than 100,000 members in the UK.
I register, and enter the murky world of two-timing technology, taking note of the warning on the site: "Not all affairs have a positive effect on a marriage." What a masterpiece of understatement.