I read the book and thought it was enjoyable nonsense. For those who haven't read it, it tells the tale of what happens when the world's worst cryptologist meets the world's most poorly informed symbologist, and they investigate the world's silliest secret society. My biggest problem with it (apart from Dan Brown's often-excruciating writing style) was that it gets all its "history" from some ludicrous conspiracy theory that was made up in the 1980s, and claims it as fact. I have no problem with a book set in a fantasy world, but the author shouldn't pretend it's true. For those who intend to read it, I recommend the special illustrated edition which at least contains some wonderful pictures.
Overall, it was a run-of-the-mill thriller with a sillier than usual plot. I'm surprised at how much interest it spawned.
I haven't seen the movie. Why would I? I know whodunnit. Audrey Tautou is an attraction, of course, but almost completely cancelled out by Tom Hanks.