GamePro has a story of a guy who found out that his wife was cheating on him when he discovered the Mii profile of another guy on their Wii console:
Tony, who served a year of active duty in Iraq, had a Wii sent to him while on tour before shipping the console back to the U.S. leading up to his discharge. He arrived home in April 2007 amid reports of his wife's indiscretions with another man. After confrontation, the wife maintained that she had only shared an innocent kiss with the man on a single occasion.
"[In Nov.] I flip through the Wii menu and visit the Mii Channel so I can peruse the many friends that I have created with the guys that I played with in Iraq," writes Tony in an email to GoNintendo. "As I go through the characters, I see there is a Mii that I have not created. It's a guy strikingly similar to my wife's [alleged lover].
"To be sure of this, I went into the Wil Message Board and click on the Calendar option. Through this menu I was able to identify the many nights my wife's Mii and this 'other' Mii Character played Wii Bowling together."