Atheists are often accused by theists that we are just as religious in our disbelief in the supernatural as theists are to their belief in the supernatural. I've always countered that atheism is precisely not a religion; it is just the negation of the supernatural. Atheism's relationship to evolution and science is by no means dogmatic. We do not worship any one philosophical or political creed. The job of science is to discover objective facts, and once it has, atheists along with many theists will believe it as such. But belief in the truth of an objective, empirical fact, is not a dogma. Therefore an atheist's reverence for Darwin, or Einstein, or strict belief in evolution is not our replacement for the religions we reject.
The problem is that religious people have such a hard time imagining a world view free from dogma that they assume that anyone who is without religion in their life, must dogmatically follow whatever beliefs that fills the void made by the rejection of religion. So the theist thinks that the atheist's religion is Darwinism and that Charles Darwin is seen as a god to the atheist, secretly worshiped at dark and dingy makeshift shrines. But au contraire, I don't know of any atheist ever, who has worshiped any historical figure as a god or any philosophy or political view as a religion. The "atheists" in North Korea for example, who are worshiping their Dear Leader as a god are brainwashed by a state religion, and you can say that North Korea is the most religious country in the world. It is true however, that some people that have left traditional religions have worshiped rocks, or trees, or fallen into some type of "spiritual" nonsense, but in a sense they are religious.
Religion is defined as "The belief in and worship of a superhuman controlling power, esp. a personal God or gods." So however dogmatic an atheist follows Communism or Darwinism or String Theory, there is no supernatural figurehead(s) to be worshiped. But the definition of religion is actually not that clear cut. What about a group of people who believe in reincarnation with out any god or gods overseeing the process? Would it be a religion? I'd say yes, if you can stretch religion's definition to include any belief in an intervening supernatural process. In this case, the deist would not be religious because their god never intervenes or needs worship.
If one strictly adheres to a philosophical creed, such as utilitarianism, you could say that he or she is behaving religiously, if you use the term very loosely. An extreme sports fanatic might be said to religiously follow and worship their favorite team. All uses of the words religion or religious here are not being used in their definitive sense, but are instead stretched to mean what they do not define. So when theists accuse atheists of being religious in some sense, they are not using the term correctly, and therefore atheism is not a religion.