The Italian Association of Matrimonial Lawyers claims that WhatsApp chats are cited as evidence in %40 of Italian divorce cases where cheating is involved.
Reportedly, a lot of these less-than-faithful spouses can't help but message their lovers, whether it's to whisper sweet nothings or send photos.
In some cases, lawyers say they've seen people juggle "three or four" partners through WhatsApp at one time, probably not how the developers pictured people using their service.
The divorce data probably isn't replicable in other countries, but it's certainly plausible.
A British lawyer survey showed that a third of divorce cases cited Facebook evidence in 2011, so there's at least a precedent; also, it only makes sense that a chat service with hundreds of millions of users would be used for philandering.
Paramours might not rely on WhatsApp quite so much in the future, though. Now that the service has true read receipts, it's that much harder to deny a scandalous affair, it wouldn't be surprising if many cheaters switch to disappearing messaging services to cover their tracks.