This is not a rumor. From Reuters:
HAVANA (Reuters) - Cuban President Fidel Castro underwent intestinal surgery on Monday and delegated government functions provisionally to his younger brother Raul Castro, the government said in a televised statement signed by the Cuban leader.
Castro, who turns 80 on August 13 and has led Cuba since a 1959 revolution, delegated his posts as first secretary of the ruling Communist Party, commander in chief of the armed forces and president of the executive council of state to his brother.
Let's hope this guy is on his last legs. He's one of world's worst dictators who has kept his citizens caged like animals. He can not leave this world fast enough.
Update: Babalu Blog is the place to be for Castro updates. Val reports that people in Little Havana are in the streets celebrating. Watch the video here. Some are convinced the announcement that he's having surgery means he's already dead.