Archives of fanfiction on the net have traditionally grouped stories according to rating (i.e. X, R, PG-13, PG, and G), so that everyone knows what to expect before they read a story. But it turns out that their use of the rating system may be illegal. A few fanfiction writers have apparently begun receiving cease-and-desist notices from the MPAA demanding that they stop using the rating system since it's the intellectual property of the MPAA. The people receiving these notices can hardly believe they're real. And other people are puzzled as well. Riba Rambles summarizes:

Some are wondering if this isn't a hoax. Not only has this practice [i.e. rating fanfiction] been going on for years without incident, but so far only smallfry individuals have reported receiving notices, rather than major archive sites. Others question the MPAA's legal standing pointing out that the MPAA's trademark specifically states its use for motion pictures, and besides there's no profit in fanfic to go after. Meanwhile, a few people are having fun suggesting useful (and silly) alternate ratings systems.

My guess is that the cease-and-desist notices are real. As with the Eiffel Tower copyright issue, it's another example of the strange lengths to which copyright and trademark enforcement are being taken. Or rather, another example of lawyers with nothing better to do.