I think we're playing the semantic game here folks. I am only an egg, but IMHO, we're confusing the word 'religion' with the word 'faith' (or dogma, as AssFace
mentioned. What I mean to say is, the similarity between atheism and religion is that they imply a faith - a belief without proof.
Religions tend to place their faith in some un(scientifically)knowable deity and/or a specially inspired doctrine. One can probably not seem like too much of an idiot making the generalisation (generalisations being idiot-making mechanisims) that an atheist has instead placed faith in themselves, or perhaps the expanded concept of humanity as a whole - such as science being grounded in certain principles and procedures which, when applied, tend to give scientists comfort in the accuracy of their observations.
Atheism, just like Christianity, is a faith. But it is not a religion.
woops, s/Sym/Sem in the title, pardon my French, and danke diotalevi