BACKGROUND:
The NYTimes philosophy blog has a piece called Philosophy and Faith, offering the following as a "philosophical argument" for the validity of faith: "An answer may lie in work by philosophers as different as David Hume, Ludwig Wittgenstein, and Alvin Plantinga. In various ways, they have shown that everyday life is based on “basic” beliefs for which we have no good arguments. There are, for example, no more basic truths from which we can prove that the past is often a good guide to the future, that our memories are reliable, or that other people have a conscious inner life."
SUBSTANCE:
Comparing religious faith to other commonly held faiths, such as faith in one's wife, or faith in humanity, doesn't show that it's rational to believe in God; it simply demonstrates the near universality of irrational thinking, meaning religion is no stupider than the other bullshit around which people base their lives. This means that the most intellectually sophisticated comeback against an agnostic is, "well I think you're stupid too" - a statement that, while usually true, is a bit of an ad hominem non sequitur. Sort of like when you have a couple of hideous gorgons arguing by calling each other ugly: the fact that the one is disgusting doesn't make the other more attractive, and seeing the two of them together, debating as though it does, might actually compound the laughable heinousness of their appearance.
As a devout agnostic in all things, I have no absolute faith in humanity, in inductive reason, or in any sort of God. However, I'm willing to go through the motions, pretending I believe wholeheartedly in the goodness of man and acting as though the laws of physics will undoubtedly hold, just because they're the best percentage bets available. When you do the same thing with God, it's called Pascal's Wager, but I've heard He doesn't honor your winnings when you make that play. As is often the case, the first step is to lie to yourself, so that you're being "honest" with everyone else; for some, this is easier said than done.