Coming home this afternoon on the bus I spotted a Christian tract sitting on one of the seats. I took it with me when I got off, so that some poor unfortunate wouldn't be warped by reading it.
In reality I suspect that tracts don't have much effect at all. Religious upbringing, personal relations, and other interactions strike me as much more likely to have an effect on one's religious choices than an easily ignored piece of paper. Of course part of the thinking of those who distribute tracts is that they, like the religious works they're based on, have some sort of God given power to effect others, that they're a magical talisman.