Many people treat agnosticism as a 'non-committal' approach to the question of God's existence - this is why it is so often treated as though it were a "third way" between atheism and theism, with each of the other two committed to some particular answer and agnostics refusing to take sides. This perspective may be mistaken, but it is common enough to merit further explanation.
Read Article: Agnosticism and Commitment

“Agnosticism is a lack of knowledge, not a lack of commitment — agnostics still either have a belief in the existence of at least one god or they lack any positive belief in the existence of any gods.”
I would rephrase that as the absence of a claim to knowledge. But that’s not my main point.
I don’t think that the law of the excluded middle applies to belief. For a period of three months in 2005, I could not call myself a theist or an atheist. If you had asked me, “Do you have a belief in God? Yes or no?” I would not have been able to give you an answer.
In my case, this was an unstable mental state. But this was to be expected; I had come from a Christian background where the weight of eternity rested on the answer to this question. But I cannot rule out that some people might comfortably remain in this indeterminate state indefinitely.
FWIW, I am a “tooth fairy agnostic.” I will readily admit to agnosticism if Ray Comfort challenges me on it, but otherwise, I am an atheist.
Then what’s the “middle” between the presence and absence of a belief?
This doesn’t mean that the belief was neither present nor absent.
Not being able to say whether a belief is present or absent doesn’t mean that it isn’t present or absent.
An excellent way to say that one doesn’t entirely know the state of one’s own mind. In that case, you can’t reliably say that you neither believe nor disbelieve.
Sounds like a person who isn’t sure if they should believe or not. That’s a radically different question from whether one does believe or not.
You haven’t established that there is some state “between” the presence and absence of belief.
I class myself as an atheist. That means I don’t believe in God or any gods. However I never say there is no god because I can’t prove it or even show it in any totally convincing way. It is the problem of proving a negative.
I like to rate belief on a scale of 1 to 9. 1 is bible fundamentalism. 9 is atheism asserting there is definitely no god. 7 to 8 is agnosticism with uncertainty either way. On that scale I place myself halfway between 8 and 9.
I can understand that previous Christian believers can become agnostic as they begin to doubt their faith. It might just be that doubters have not yet been exposed to enough evidence or enough argument to bring them to total disbelief.
@Austin – Let’s just call it Schrödinger’s God belief.