The working definition of Religion I was using is as follows: "a particular system of faith and worship."  Being a system of faith as you yourself admit, atheism is indeed a religion in accordance with this recognized definition.  I do understand, however, that you may have been arguing from an alternative definition of religion such as: "the belief in and worship of a superhuman controlling power, especially a personal God or gods."  From that definition, of course, you'd be correct.  So, instead of trying to split hairs, we are both correct, atheism is or is not a religion depending on the definition of religion one ascribes too.  But either way, I feel the distinction some atheists try to make in this regard, is nothing more than semantics as both atheism and other religions elect to believe in that which cannot be proved nor disproved.  As such, atheism and other religions are equally dependent on faith.