I think I said this before, but it just came up in discussion tonight. Agnostics cannot say they believe in God, therefore they are a subset of the set of all atheists. In no way can they be called believers, they are merely in denial of their atheism. They cannot be a subset of the set of all believers because their set does not intersect with the set of all believers, they are non-believers, their belief is non-existent, it is a dead parrot.
I don't believe that anybody educated and conversant with manifest reality truly believes in God. Anyone who claims to is only fooling himself or herself, but they all get together and play "let's pretend" and "la la la we're not listening".
I'm not happy that there is no God but then as somebody said, "if God lived on our street people would break his windows."
Update 22/2/2016: Agnosticism and Atheism have been divided by some philosophers into Agnostic Atheism (don't know what's what but don't believe in gods) and Agnostic Theism (don't know what's what but accept the possibility of gods).