I agree with all those who say that the Da Vinci Code is fiction. However, I question the factoid at the very beginning of the book: "All descriptions of artwork, architecture, documents, and secret ritual in this novel are accurate." Are they? I think there would be far less controversy if he had not included this one page. Consider one example--and that is the purported 666 windows in the Pyramid at the Lourvre put there at Mitterrand's explicit demand! Fact is there are windows, but there are more than 666. No Satanic conspiracy there. Do a search.
Look at a picture of Leonardo's Last Supper. There are 13 people represented. If John is really Mary Magdalene as Brown claims, where is John? There should be 14 people if that were true. John would certainly not be excluded from the painting. Remember that John is the disciple whom Jesus loved and is depicted at Jesus' side and who leaned back against Jesus' chest in John 13:23-25. See also John 19:25-27. Besides, Leonardo left us a description of who is in this painting. It does not include Mary Magdalene.
It is not only religious people who have objections to some of the things that are conveyed as truth in this book. See "Leonardo scholars remain faithful to the scientist. The Da Vinci Code does a disservice to one of the world's most creative thinkers and all his loyal fans."
http://www.stnews.org/books_2833.htm
In the Fact section Opus Dei is called a sect. False. It is accepted as a part of the Catholic Church as are the Franciscans, Dominicans, Jesuits, etc. How is it a sect? They are not a breakaway. Silas, one of the main actors is depicted as a monk. Fact is, they are not monks as they do not withdraw from the world, but rather work and live in it. The people who live at their headquarters are not monks. People might criticize them for unpopular practices of mortification but they are certainly not bloody as depicted by Brown. Whatever criticisms may be leveled at the members, murder is certainly not one of them. Yet, because of the Silas character that is what most people will associate them with. Let's give Opus Dei the opportunity to give their side of the story.
http://www.opusdei.org/art.php?w=32&p=7017
So, yes, it's fiction--but that introduction is what, it seems to me, has created an issue.