i, like many others, bought Da Vinci coz it was a bestseller for weeks, although i would like to believe that people are like sheep, one following the another.
as a piece of literary art, Da Vinci code is nothing special: a typical murder story, the detective being a key suspect, chased by the french equivalent of the FBI, trying to find the secret behind the murdered victim. in terms of plot development, character depth, literary skill if you will, it is probably on the same level as the many Clive Cusslers, Tom Clancys out there.
the reason i believe it is such a bestseller is because some of the 'secrets' discussed are so bloody controversial... the reaction has been so great that there have been many 'cracking the da vinci code' books published (pro-christian books highlighting the errors/misrepresentations made).
but then again, this just goes to show two things: "religio nihil est mihi"; some people are easily led to believe as fact the work of the fiction that they read.