Pew Research recently reported their findings that religious "nones" are not only growing, they are becoming more secular. This should come as no surprise.
There are good reasons why the very term "religious" is developing a negative connotation in our society. We have the divisiveness of hard line, literal "fundamentalists" types to thank for this. The existential and political positions they tend to espouse represent all that is provincial and immature when contrasted against the opportunities for, and imperatives to, the more sophisticated interpretations to which our multicultural and globalized society is calling us.
I believe the trend toward the a "spiritual but not religious" stance results from young people growing up in less authoritarian milieux where independent thought is encouraged and, at least online if not in person, they are exposed to people from multiple cultures and religions. This kind of universal exposure, together with more recent scientific findings that ours is an expanding, constantly evolving universe, makes any single religious doctrine providing fixed existential answers sound provincial and preposterous.
If religion is to survive, the religious message will have to evolve toward expanded and more sophisticated interpretations. The rising number of "nones" gives evidence that so far, it has failed to do so.