Agnosticism was coined by Thomas Huxley, so any discussion should keep in mind his definition:
Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle … Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable.That works for me.
That said, Steve Brust makes some fine points in Steve vs St. Thomas, which he just characterized on Twitter as "New blog post: Why I'm not an agnostic."
ETA: Because I just love to quote Malcolm X: "Since I learned the truth in Mecca, my dearest friends have come to include all kinds — some Christians, Jews, Buddhists, Hindus, agnostics, and even atheists! I have friends who are called capitalists, Socialists, and Communists! Some of my friends are moderates, conservatives, extremists — some are even Uncle Toms! My friends today are black, brown, red, yellow, and white!"