I am an agnostic. I do not think I am smart enough to truly know the existence of God. I also do not see God's existence as likely enough to justify following a religion, and could probably never follow a religion that required me to be absolutely certain.
I definitely respect religions for their humanist aspects, though. Even if I can't believe it, I try to do my best to respect belief.
"I don't believe in magic. But I do believe in interpreting coincidence exactly the way you want to." -Sherman Alexie