Facebook has filed trademark lawsuits against sites like Teachbook and Lamebook, which fall under a legal gray area. Nothing is gray about what FriendFinder Networks (owned by Various Inc.) has done with their very naughty website FacebookOfSex.

While the site in question includes profiles similar to Facebook, the site encourages people to display, er, adult pictures and videos. Facebook wants damages and control of all the various domain names that the site operates on.

Source: PaidContent {link no longer active}