This one incident has had so many variations and urban legend-ish twists. This article itself even incorrectly lists the date as 1945 in one place, which is a common twist on the story, but incorrect. (This computer didn't even come into existence until 1947, so the bug couldn't have been found in 1945). For any know-it-alls who like to one-up people with the correct facts, here's the truth behind the story, best I can figure out:

• This is indeed a real log entry book from September 9, 1947 (not 1945, as is sometimes reported)
• Grace Hopper did not write the log entry book
• Grace Hopper did not find the bug. She wasn't even there that day
• Grace Hopper did make the story famous, though. Even though she wasn't personally involved, she found it funny, and liked to tell it, which is how she got associated with the story
• This was not the first usage of the word "bug" (obviously, since "First actual case of bug being found" wouldn't have been funny). The earliest recorded usage of "bug" (in an engineering context) was Thomas Edison in 1878, but it surely predated him, as well. It was in common usage among engineers in the early 20th century
• It was not the first usage of the word "debug", as is often attributed. We have a record of the word "debug" being used in 1945. (Maybe this is why some versions of the Mark II story are sometimes given as 1945). "Debugging" was used in the aviation industry before the software industry
• The earliest recorded usage of the word "debug" in the context of software is 1952, but again, it probably predates its first record. Who knows if the word was already in use in 1947!