The Center for Social Media at American University has a story about Turnitin, a site used to catch plagarism, citing Fair Use to win a case against students who sued them for taking intellectual property. The irony was not lost on Patricia Aufderheide, who concluded:
So let the students—and the teachers—take a real lesson from Turnitin. Quoting from other people’s copyrighted work is sometimes, even often, fair. Not all copying is cheating, or copyright violation.