One of the most frequent criticisms of those who believe that life and the physical universe are intentionally designed is that those who believe this cannot adduce any mechanism for how the designer would have accomplished the feat. Since design theorists can't posit a means by which the designer would have created a universe or biological structures and organisms the design theory is said to be unscientific. It may be philosophy, skeptics concede, but it's not science. Science is based on empirical evidence, not faith.
This last claim may be so but if it is much of what passes for science is no more supported by empirical evidence and every bit as faith based as is intelligent design. This is especially true of the belief that life arose purely through the laws of chemistry and chance. Here's part of what Paul Geim at Uncommon Descent says about the problem:
[This belief] is heavily faith-based. We have no experimental evidence for this belief, and the theoretical problems appear insoluble. We have here belief against all the evidence, analogous to the most daring leaps of religious faith imaginable, that is to say, faith not only without evidence but in the teeth of evidence. And it is even worse; there is no appeal to a God Who could reasonably do the feat that needs explaining. It is a miracle without God.
The rationale that I have seen for this leap of faith is usually that "science" has solved all previous problems and will solve this one too. But this argument is wrong, on two counts. First, even if successful, it would only establish that there was relative parity between the argument for the supernatural origin of life and those for abiogenesis (the origin of life from non-life). We would still be completely dependent on faith to believe in abiogenesis.
Second, and perhaps more importantly, "science" has in fact not solved all previous problems. Science has come up to a stone wall regarding the origin of the universe. In fact, "science" has come up to several difficult obstacles, issued promissory notes, and moved on without actually solving the problems. The origin of the Cambrian fauna is something that non-interventionalist evolutionary theory has simply postulated without fossil evidence. The origin of the flagellum in a step-by-step manner has never actually been demonstrated (the best try, that of Matzke, was actually a leap-by-leap explanation, and even then without any experimental evidence to back up his scenario). This insistence that nature must be self-contained is in fact faith against the weight of evidence.
Geim has much more to say about the problems inherent in any naturalistic explanation of the origin of life (OOL) at the link.
For more on the things scientists take on faith, often with little empirical warrant, see my letter (May 2006) to First Things.
RLC