The Council for Secular Humanism has put out a report by Greg Paul, “Is The Baylor Religion Study Reliable?”. It criticizes the recent book published by Baylor, with lead author Rodney Stark, that reported that US religiosity remained stable and that there were no signs of secularization.
Paul points out some very serious errors in the report. (I can’t say I’m wholly surprised; I’ve lost a lot of respect for Stark over the last few years.) I’m less confident about the picture of secularization he presents. My reading of his data (worth exactly what you pay for it; I’m not a sociologist) is that while old-fashioned, organized religion is clearly in decline in technologically advanced nations, there’s not necessarily a corresponding gain for a stance that is skeptical about the supernatural.
The Baylor people lump everyone who is not a convinced atheist together into a religious camp. (They’re not the only ones; I’ve read sociologists who argue that people who express an interest in “the meaning of life” in polls show signs of religosity.) But Paul lumps too many types of dissenters from traditional religion together. Throwing atheists and agnostics together might be justifiable, though I even wonder about that, since popular ideas about an agnostic label are remarkably mushy. But just expressing a degree of doubt does not put anyone in the nonbelief column. Also note that the survey data Paul discusses focus exclusively on conventional theistic beliefs. Large numbers of the ostensible nonbelievers counted, I would guess, have shifted to a more individualist style of spirituality, with a less personal and authoritarian concept of God. This is, in a sense, secularization, but it also does not represent a decline in supernatural belief.
My guess is that the secularization trend represents a muddled middle gaining ground. Westerners are not so much becoming atheists as becoming more individualistic in spirituality, more secular in public behavior, and less orthodox in supernatural beliefs. Naturalistic atheists in particular remain a tiny minority.