I am convinced we should not take the Da Vinci Code seriously, life is too short. However I cannot resist a comment on all the rubbish surrounding it. The trend, in the Holy Blood and the Grail as well as numerous other books (for eg ones on the cathars, the "gnostic gospels" etc) to present the gnostic tradition of the early centuries of the Common Era as a supressed progressive strain of Christianity is false and misleading. Its like looking for the secret room behind a picture rather than looking at the picture in context.
Interestingly orthodox Christianity would have some of the same criticisms of gnosticism that the AWL reviewer has of all the fascination withthe Da Vinci Code, its esoteric and 'mystical' approach and its ideological anti materialism.
There are even some who have traced gnostic influence to 20th century Nazism.
I do think it is interested to examine the apparently increased interest (including in progressive circles) in religious esotericism since the end of the 19th century but this should be done in a systematic way that considers its place in the history of ideas and looks for material causes for it. I think it would be profitable for someone to consider the impetus to 'mystical' explanations in the context of the reappraisal of the 19th century model of science with the development of 20th century science. Or maybe from another viewpoint to consider what sociological value a 'mystical' rather than an orthodox religious or 'rational' explanation can provide for certain groups of people in certain circumstances - perhaps the US would be a good place to start!
There are interesting parallels of the fascination with secret conspiracy theories within the development of the 20th/21st century religious tradition itself, such as a significant renewed interest in spirituality, both within and detached from orthodox religious tradition. This is so mainstream now that I recently received a flyer for a seminar on spirituality for business! Other trends that seek to recover spiritual traditions, Goddess worship, creation centred spirituality, even the concept of gaia, could be best classified as containing revisionist readings of religious traditions that in general undermine church authority and give more room for progressive ideas.