In fact, straight from American Airlines:
http://www.aa.com/i18n/agency/Bookin...p&locale=de_DE
Specifically: "Although the issuance and usage of hidden city tickets is
not illegal in the sense that one could be fined or sent to jail by the government.."
They then claim that it's unethical, though I'm not sure I want to take my ethics classes from an airline.