I am nearing completion of Robert Putnam's American Grace, which has much to commend itself. Religious leaders should read it mainly for all the revealing data.
One objection I've had with the book is the way it measures "religiosity." The standard it chose was saying grace daily before meals. The reason I find this an odd choice is that I believe it selects out certain more pietistic forms of religion. I know many deeply religious people who don't say grace before meals every day, but live out their religious faith with a host of other religious factors. I'm not sure what criteria they could have chosen, but I do think it colors their data, in that throughout people high religiosity appear more conservative, less tolerant, etc.
One thing that does reveal the inadequacy of their measurement is when they discuss volunteering. People with higher religiosity volunteer more. They then remark that it is surprising that liberal mainline Protestants volunteer to a higher degree than their religiosity. No, I think that for many liberal mainline Protestants their volunteering would be one of the core spiritual practices evidencing their "religiosity."