The dictionaries don't really agree with me but I think there's a subtle difference between being "sure" of something and to be "certain" of it. The former implies to me very little doubt, whereas the latter implies no doubt whatsoever. Therefore, like most people here, I'm sure there's no God, but I'm not certain, i.e.I'm your typical 6.9er.

Along the same lines, I'm sure the sun will come up tomorrow, but I don't think I'm certain of it as some very tiny possibility exists that something will affect the earth's rotation in my lifetime.

That said, once again people with a religious perspective show how they just don't understand us. No atheist can intellectually claim certainty about the existence of god(s), since we think all knowledge is provisional and we're always ready to change our mind if evidence were to be presented. Religious people, like politicians, think this is a sign of intellectual weakness rather than the intellectual strength and integrity we consider it to be.

I think we understand their position so much better than they understand ours.