A collector of rare books ran into an acquaintance who told him he had just thrown away an old bible that he found in a dusty, old box. He happened to mention that Guten-somebody- or-other had printed it.
“Not Gutenberg?” gasped the collector.
“Yes, that was it!”
“You idiot! You’ve thrown away one of the first books ever printed. A copy recently sold at an auction for half a million dollars!”
“Oh, I don’t think this book would have been worth anything close to that much,” replied the man. “It was scribbled all over in the margins by some guy named Martin Luther.”
via the Humor jokes blog