Dan, asked me this question about my post yesterday and I found my answer getting so long that I decided to post on it. I haven't done any additional research so this is my answer off the cuff.
Perhaps I take a narrow definition of religion, but I think it's the belief in a god or gods, and supernatural events which, though outside of nature, can influence and change nature. It also includes a set rules, codes of conduct, moral instructions (which sometimes seem inconsistent) and explanations for the universe which often rely on super-natural causes. Some people take a more personal road to spirituality which doesn't fit into any particular religious framework.
Atheism by it's name, means that one does not believe in god or a predefined code of conduct, book of the universe, and generally that goes for other supernatural entities/descriptions. In my mind atheism is a bit like Occam's razor because you don't look for additional supernatural causes for things, but look for causes within one single naturalistic framework.
Here's a question, what is the difference between religion and believing in Father Christmas or any other supernatural entity? The lack of belief in something for which there is no (reliable) evidence or argument is no different than not believing in a whole host of other possible beings/entities for which there is no evidence. For example, should I believe that there are sea urchins flying around the moon? (I realise that the concept of god is considerably more sophisticated)
Obviously a religious believer, may believe that the evidence and arguments are sufficient, or they suspend normal ways of discovering knowledge thus making a decision to believe. Others yet, have made no decision about it, but believe because they have been brought up in a religious framework, hence their whole way of thinking exists within this framework.
However this does remind me of a quote that says: Absence of proof is not proof of absence. But in that case wouldn't it be better to take a sceptical point of view, otherwise one could start believing in all sorts of things?
But really for me it comes down to the fact that from my thinking and understanding of science, philosophy and human behaviour and history, I don't think it makes sense to believe in religion. I admit that god is much more difficult issue, and perhaps I am more agnostic on that point. My agnostism about god could however be caused by the fact that we can define god in any number of ways. The ways that make more sense to me, by their very nature make it impossible to prove or disprove his/her existence, i.e. unfalsifiable. If I describe god as a being that exists separate from the universe, does not obey the laws of the universe and does not interfere (by my own observation) then how can I prove or disprove it?