LEJ, I think that depends on which form of Christianity you're talking about. As far as I know, protestants don't pray to Mary the way Catholics do.

Organized religions to a large extent reflect societal norms. Problems occur when a society adopts new attitudes about right (and rights) and wrong and the religion doesn't change. Some people argue that the bible was written with divine guidance, and therefore change and adaption of the religion are impossible. People base their beliefs on what makes sense to them, and if a religion doesn't make sense, it will lose believers.