In anticipation of the upcoming movie, I've read "Da Vinci Code".
If the book or movie get people thinking about their spiritual beliefs and spur open and reasonable discussions about it, then I think it can be quite useful. Certainly the Christian church is smart enough to leverage pop culture to fill seats on Sunday or in their Alpha courses. "Passion of the Christ" was extremely useful to them for that, although I expect that "The Da Vinci Code" won't be quite as useful, since its story is complicated and multi-layered and not of a kind that is easy to refocus into a positive message for Christian beliefs. Brown's book essentially makes the Catholic Church the big bad guy, responsible for completely re-spinning Christ to suit their own needs.)
There is a lot of criticism of Brown's novel. I have recently read a book (one of the "Rough Guide" series) that flatly denies the claims of Pierre Plantard and says that all of his "Priory of Sion" evidence is fake. Indeed, Mr. Plantard (who passed away in 2000) seems to have very little credibility, and likely no connection whatsoever to the fabled Meringovian royal bloodline, counter to his claims and manufactured documents, much of which influenced the research of Leigh and Baigent in their 1983 book, Holy Bood Holy Grail. Their book was in fact a major inspiration for Dan Brown's novel "The Da Vinci Code".
The possibility of Jesus Christ being a mortal - a human - leader, is appealing and makes total sense to me. I've never been much on mysticism or things like life after death. However, human history proves we have a fascination with the supernatureal - with the idea of beings with powers and levels of existence greater than our own. Like children, we may look for their to be a greater authority to guide us or lead into our future. Our sense of "faith" tells some of us that this must exist, and that we can touch it and depend upon it. As an individual, I have never felt this way. I see that humans lead other humans around, for a variety of selfless or selfish reasons. My experience says that the mysterious is just something we couldn't explain when we saw it. To me, it does not mean that it can never be expained or cannot be understood by humans.
The authors of "Holy Blood, Holy Grail" also wrote a book about the discovery, interpretation and politics linked to the Dead Sea Scrolls. Generally, I agree with their (and other researchers') claims that biblical revisions have occurred throughout history to suit the political/social needs of various rulers or of the Christian Church.
For what it's worth, I think "A History of God" by former Nun Karen Armstrong, is also an *excellent* overview of the historical development of "God" as interpreted by Christianity, Judaism, and Islam.