Some general points on the concept of faith: I've personally found that those most "faithful" of people are almost always looking for a 'safe' way out. Faced with uncertainity and an underlying fear that they'll be damned to hell if they don't believe unswervingly, they are most hostile to any rational analysis of their religious tradition.
That said, there are more understandable and self-respecting stances to take. Danish philosopher Soren Kierkegaard essentially agrees with agnostics in that theology is impervious to human reason, claiming that all religious belief requires a "leap of faith", much like that leap of faith taken by Abraham when God instructed him to kill his son, Isaac (Ishmael in the Qur'an). Although it pained him to obey his command, Abraham was fully prepared to sacrifice Isaac. There is a point, believed Kierkegaard, where one must realise the tenuousness and unverifiability of their beliefs but nevertheless stand by them. I can respect this stance, which doesn't claim any absolute truths about the existence of God.
One more point to ponder: aren't all believers agnostics at heart? Think about the term 'believer' - it's one who accepts something as true or real. They are not 'knowers'. The mere fact that one believes does not preclude them harbouring doubt, however miniscule - in fact, I'd say you'd have to be pretty uneducated and narrow-minded not to.