The secular is used and abused. It has limited utility, I think, for Christians working out their way in North America, but that small range of usefulness is very significant for what work it can do.
I love sociologists, anthropologists, and statisticians. They do hard work, ethnography, and train to carefully study human life present and past. But their work is often used and abused. Friedrich Nietzsche wrote a remarkable essay on the use and abuse of history and it is his cues that I will follow. There are quite a few definitions of secular, conflicting accounts of why or how much there is a secular, and even lots of arguments about the end of the secular in our day with the return of the religion, arguments that conflict with "end of religion" theses put forward by other authors. A good survey of these is in Varieties of Secularism in a Secular Age.
In general, there are two patterns that I think Christians have taken to use the secular: "take back" or "eliminate." I think there is a third that tends to be "fire alarm."
Taking back the secular means to reclaim what is lost. This view sees secularism as basically the loss of the religious trademarks or some sort of essential Christian "core" that needs to be taken back. Example: Christmas or battles of yoga as a religious exercise or just exercise. Liberal Christians do this just as much as others who want to "keep the Christ in Christmas" when they want to show how some secular movement is congruent with what they take to be Christian aims. This form of the secular is usually experienced by religious people as a kind of alienation of their goods, their intimate stuff made fun of and turned inside out in the culture. Or it is a sense that they are sharing what is intimately theirs with people who disgust them.
Elimination of the secular can go along with taking back but is different than that use of the secular since it usually means that the secular should be replaced with the sacred. The sacred is usually taken in this sense as a set of cultural artifacts or practices that need to be purified or reclaimed.
The final use of the secular I take to be sounding the fire alarm. This is used by many to argue that the advance of the secular, no matter what that means, is to spur Christians on to some action, to leave the house, to abandon the dried husk of Christendom, or to urge older American Protestant views of Christianity (awakening, sectarianism, or evangelical church growth)
The problem with each of these uses betrays the sense of what the secular and sacred are in each case, a subject that deserves more attention. Lots of work on the secular talks about the "re-sacralization" of modern life or the "post-secular." This means that the boundaries between what we call sacred and secular are far from stationary. And that is worth another look in a later post.
Addendum: Elimination also occurs when one simply states that "there is no secular or sacred," when one sidesteps the distinction all together.