I used to describe myself as an agnostic, but now I describe myself as an atheist. What changed was not my faith (or lack of it) but what I understood those words to mean.
I used to think that the meanings were as follows:
Atheism: I believe there is no god.
Agnosticism: I neither believe nor disbelieve in God.
But I know think that the following definitions are more accurate:
Atheism: I do not believe that there is a god.
Agnosticism: I have no opinion about the existence or nonexistence of God.
Specifically, I don't think that there is a god but would rather avoid describing myself as having any sort of "belief" one way or the other, because that word carries some implication of "belief without (or despite) evidence". While it's impossible to ever prove with certainty that there is no god (or indeed to prove with certainty anything other than "I think, therefore I am") I think that there is a great deal of evidence that there is no God. I'll take a look at some of this evidence tomorrow.