On the surface, the site isn't much different from a lot of forum pages. The members, however, have proven to be a cruel and ruthless bunch.
Supermensa have openly admitted to bullying many people, and harassing and degrading them as well. They have designed a wiki for anyone they don't like and have been known to post IP addresses in order to spam mail and harass anyone who doesn't agree with them, insults them, makes a request of them, looks at them funny, or anyone else that they don't like. They proudly declare they had brought people to tears simply for "LULZ," as one of the "top" members of the site called it. Here are a few examples of the people they have victimized.
http://supermensa.org/wiki/index.php/Riggs4827
http://supermensa.org/wiki/index.php/Jordan
http://supermensa.org/wiki/index.php/TWS
In all fairness, the site gets all of its information on its subjects legally through public channels, with Google searches, etc, however, they continue to harass them after the fact, and on top of it, they refuse to take down posts when such information could be harmful to the individuals in question. All in all, they're bullies. They've been bold enough to bully someone who reported them right here on this site and they will likely attempt to do the same to me.
They are needlessly nasty and cruel to those they victimize and when their victims attempt to defend themselves they claim they are merely adults having adult conversations, all the while paradoxically behaving like schoolyard bullies.
UPDATE: And of course, there's this: http://img153.imageshack.us/img153/9805/74587302.jpg