I am currently reading Daniel Barenboim's memoir. Here is an anecdote about Dmitri Mitropoulos, who in his opinion had "the most phenomenal memory of anyone I have ever met."
"The story is told that when he was Music Director in Minneapolis and was supposed to conduct the world premiere of a new American piece, the orchestral parts did not arrive until the day before the first rehearsal, and the conductor's score never arrived at all. So he took the orchestra parts home and spread them out on the floor the way an orchestra sits. He then memorized the piece overnight and the next morning rehearsed it from memory."
'Nuff said?