ABSOLUTELY THIS.
I was horrified by the fact that my wife was using her laptop to flirt and cyber with a guy and sneak around and fuck him. But, being on our network, I knew how to connect to it and read the logs.
I was saving them for the divorce (without her knowing) and found myself getting equally turned on as I was reading them.
Never needed to use them against her, and she still doesn't know I have them, but they make great jerk-off material.