There is some recent research that adds to the long-known fact that Americans inflate their religious participations in surveys. It appears that in terms of frequency of attending services, Americans are not such an outlier compared to other post-industrial nations after all. Shankar Vedantam suggests that this indicates that Americans are actually not significantly more religious than Europeans.
That, however, strikes me as relying too much on one type of research instrument as much as relying solely on survey-based methods. Religiosity is not a simple thing; it’s not even a single thing. In the overall (average and coarse-grained) picture, I think it remains safe to say that Americans remain noticeably more religious than western Europeans. I don’t expect sociology of religion texts to be rewritten, particularly since it’s been known for quite a while that Americans exaggerate their attendance at services.