Following the list of things you know not of Leonardo da Vinci, there is another site with examples of the mistakes Dan Brown made in his book The Da Vinci Code.
Warning: Spoilers are ahead
_(The Da Vinci Code, by Dan Brown. Book cover.)_
# Sophie imbeds the GPS receiver in a bar of soap, breaks a restroom window and throws the soap onto the roof of a passing truck. In reality, the restrooms of the Louvre have liquid soap, just like most other public restrooms. And also cccording to a “Da Vinci Code” tour guide, the restrooms in that part of the Louvre do not have windows.
# Langdon says that Saunière, a devotee of the ancient “sacred feminine,” was interested in Wiccan relics. However, Wicca is a modern religion, not an ancient one.
# The novel implies that the Louvre has one curator. It really has a staff of 60 curators in eight departments. The “Mona Lisa” has its own curator.
# France has used the metric system for 200 years, but Sophie, who has lived in France for most of her life, says the GPS dot is accurate to two feet. She makes another gaffe later when she claims that her Smart Car travels 100 kilometers per liter of fuel, just before she says the American Embassy is only two miles away. A hundred kilometers per liter — or 239 miles per gallon — is an impossible figure. Smart Cars get closer to 60 miles per gallon, or 21 kilometers per liter. Twenty one kilometers per liter is approximately 100 kilometers per gallon, though, which is a real metric mix-up.
# Approximately 50,000 people — men and women — died during the years of witch hunts, not 5 million. Dan Brown must be read 2 extra zeroes somehow.
# The Priory of Sion is a fictitious organization, founded and publicized by Pierre Plantard in 1956.
# Nothing in the Bible or any other existing historical document proves that Jesus was married to Mary Magdalene. At the same time, no existing document proves that he was not.
Read more at source: HowStuffWorks
Also, JayDax did a study on The Last Supper by Leonardo Da Vinci, quite interesting read too if you read The Da Vinci Code.