Einstein's Views on Religion and Ethics

Continuing on the religious theme, came across an interesting write up on Wikipedia today, about Einstein's views on atheism and agnosticism. Old Alby labelled himself an agnostic, saying that "the problem involved is too vast for our limited minds". He firmly believed in ethics, saying "The most important human endeavour is the striving for morality in our actions...Only morality in our actions can give beauty and dignity to life...A man's ethical behaviour should be based effectually on sympathy, education, and social ties and needs; no religious basis is necessary." Apparently he didn't rate atheists: "I do not share the crusading spirit of the professional atheist whose fervor is mostly due to a painful act of liberation from the fetters of religious indoctrination received in youth". Interesting!
I've been thinking lately that atheism, as the opposite of belief in God, is an act of belief in and of itself, believing in the non-existence of God. In the same way that an atheist would reject christianity's certainty that God exists, how can the atheist be certain that God does not exist? So where does that leave me? As an agnostic - I guess.