[Anitius Severinus Boethius]

But there are no actual "If you're caught committing adultery, you are fined or jailed" laws, right?

This is a good place to start. Start reading on the last paragraph on page 19 of this Supreme Court decision. You will see that as of 1996 the District of Columbia and 25 states had laws against adultery. Not just listing adultery as a charge of divorce, but actual statutes against the act itself.

http://supreme.lp.findlaw.com/supreme_court/briefs/02-102/02-102.mer.resp.pdf

[Qwerty]

"You will see that as of 1996 the District of Columbia and 25 states had laws against adultery. Not just listing adultery as a charge of divorce, but actual statutes against the act itself."

Interesting. I wonder if anyone has ever been charged. You couldn't challenge it until it was.

Personally, I don't like the idea of police arresting people who cheated on their spouses.