Why do People Leave Religion?

This is a question that has fascinated me simply because it is one that I cannot answer. I have never been religious so I have never technically left it. Now logic, reason and rationality prevent me from taking it up, but why do people leave?

What initially triggers the doubt? What pushes people “over the edge” to completely leave?

Is it becoming acquainted with logic and reason, is it learning the counter arguments or is it as a result of emotional reactions to e.g. religious hypocracy or abuse? I have heard good arguments for many reasons, and I’m not sure if anyone has done any formal research on this issue (if anyone knows of any research please post a link).

I have started a thread on the forum, if you have been previously religious what has done it for you?