I just wanted to clarify that atheism has 2 camps.
I am what some people call a "lower-case-a-atheist", where I simply have an absence of belief in a god or feel there isn't enough evidence.
Then there is what some people cal a "capital-A-Atheist" who believe that there is no god.
Agnosticism, in the strictest terms refers to religion, not god. So you can be an agnostic who believes in god (usually called diest or thiest) and you can have a religion without a god, such as zen budhism, or people who follow religious ceremonies, but don't believe in god.
It's really up to the individual what they call themselves. I wouldn't try to make parameters for christians to determine their christianity.
I am an organizer for an atheist group here in Sacrament, and I consider myself an agnostic and an (lower-case) atheist.
What the former guest said about atheism is accurate, in my opinion.