Thanks to mrsr58 for the heads up, there's a great article (despite some inaccuracies) from The New York Times about "Supernatural". It's titled Heaven, Hell, Brothers and an Impala. Here's an excerpt:
In the absence of “Battlestar Galactica,” which ended its run two years ago, “Supernatural” is easily the most theistic series on television, its worldview rooted in the idea that a war is raging between heaven and hell. During the series’s first three seasons Dean, who speaks as if he were trying for chief-executive authority by forcing his voice down a few octaves, had been an atheist. (Let’s leave aside the fact that there are far easier avenues of employment for nonbelievers than combating Satan.) But saved by a surly angel during a bout of spiritual ugliness in the fourth season, Dean reconsiders his thinking.