I remember (I scarcely have the right to use this ghostly verb) the tale "Funes, the Memorious" from the argentinian writer Jorge Luis Borges, about a man who was able to remember EVERYTHING: "In effect, Funes not only remembered every leaf on every tree of every wood, but even every one of the times he had perceived or imagined it."

http://evans-experientialism.freewebspace.com/borges.htm