Although I was tempted to respond immediately, I decided to allow some time to pass in order to seriously consider whether my post was, in fact, picayune. I've decided that it wasn't, so I thought I'd take space here to further develop my thought on the matter.
I agree with Michael that the intent behind using the phrase in question as a title of an apologetics book was most likely to humorously display the irrationality of atheism. But that only serves to illustrate my point. Used in that context, "faith" is that which is required in proportion to the irrationality of a belief. The more irrational the belief, the more faith required. By saying "I don't have enough faith to be an atheist," I may mean "Atheism is irrational and therefore I can't bring myself to believe it," but what I'm actually saying (and what the atheist will understand me as saying) is that faith is the capacity to believe the absurd.
Actually, my purpose wasn't to target the book by Norm Geisler and Frank Turek. I've not read it but from what I've heard from those who have, it's very good. My concern was, and remains, Christians carelessly using biblical terms in unbiblical ways, thereby perpetuating and contributing to misconceptions about biblical Christianity. We often talk about the importance of context for understanding a particular verse. Likewise, a Christian's understanding of the meaning of such words as "faith" should be derived from the usage of that word in the entirety of Scripture. There is, in other words, a canonical context that should govern how we define and use words like "faith." This is a function of biblical authority. When we converse with those whose concept of faith is contrary to that of the Bible, and adopt that usage ourselves, we are neither aiding them in their understanding nor faithfully representing the biblical perspective we are seeking to commend.
Francis Schaeffer frequently noted the ambiguity of the word "god" and the need for Christians to clarify what they mean by it. He writes in The God Who is There:
As Christians, we must understand that there is no word so meaningless as the word "god" until it is defined. No word has been used to reach absolutely opposite concepts as much as the word "god." Consequently, let us not be confused. There is much "spirituality" about us today that would relate itself to the word god or to the idea god; but this is not what we are talking about. Biblical truth and spirituality is not a relationship to the word god, or to the idea god. It is a relationship to the one who is there, which is an entirely different concept. - Volume I, The Complete Works of Francis Schaeffer, p. 159The point Schaeffer makes about the word "god" is applicable to the word "faith." The Christian's concept of faith is constrained by God's revelation in Scripture. Of course, we can't prevent unbelievers from attaching alien concepts to biblical vocabulary. We can, however, do all in our power not to encourage such unbiblical thinking by refusing to adopt its linguistic practices ourselves.