In a chapter (in Acts of Faith) entitled “Secularization R.I.P” Stark and Finke provide a lot of evidence that challenges the secularization hypothesis – including historical accounts of the impious behavior of church “leaders” during Europe’s “religious” past. Like Smith, their claim is, briefly, that it is state involvement in religious markets that discourages piety and that these patterns were in place long before modernity brought about lots of resources to distract people with. In The Churching of America they go on to argue that after the onset of competition in American religious markets there was a huge growth in piety throughout the 19th century. In addition, Gallup polls have shown that most indicators of religious belief have been, essentially, flat since the first half of the 20th century (though I admit some polls say otherwise).
So, I suppose I would find the Pew study more convincing if it controlled for interference in religious markets and/or used changes in income and changes in the importance of religion.
Finally, I can’t resist adding that I believe that many devout followers of Christ in the church circles I travel in would say that “religion” isn’t very important to them – their relationship with Christ is, but “religion” isn’t (I admit, I think they’re being a bit cheeky, but there you have it).