Coming soon to the Internet, .xxx domain names for porn sites. But if you aren't in the porn business, you don't really want your name associated with an .xxx domain name. Which explains why universities and businesses are (or should be) snapping up .xxx domain names to protect their brand. At $200 a pop, it makes sense. Even assuming you could defend your trademark through legal action, it's much cheaper just to own the site.
HT: Legal Blog Watch