Mike Cope got the ball rolling here with a post on doubt. I've included my comment below.
Doubt may be what saves me from unbelief - or maybe I should say misplaced belief.
If it were not for doubt, how many false beliefs would I maintain with the certainty that they were actually reflective of God? And what is belief in something false but an insidious and dangerous kind of unbelief?
My experience, riddled with doubt as it is, tells me that God gives us the gift of doubt so that we will have good faith and not settle for bad faith. He allows doubt in ours lives not because he takes any pleasure in our suffering, but as a way of loving us away from that which would cause a much greater suffering.