My 'conversion' to atheism was pretty boring actually. I went to a Catholic church, was baptised, confirmed, and had my First Communion before I turned 13. In the meantime, I was also going to the Buddhist Temple with my father.
I knew my father did not believe in god and when I went to church and heard all the terrible things that were supposed to happen to non-Christians, I took a harder look at Christianity. My heart would not reconcile the reality of a loving father who would end up in Hell.
I had always been interested in science. Asking questions and requiring answers came naturally to me. Even as a young kid, the whole god thing never made much sense to me. While I enjoyed some of the stories in the Bible, they were nothing more than your average children's story to me. I sat in the pews or at Catechism and all I heard was blah blah blah. The Bible held no interest for me whatsoever.
Once I turned 13, I was given the choice to continue to go to church or not. I did not go back except to make my mom happy on holidays. I never even made it to my first confession because it didn't matter one iota to me, or ever got to eat one of those wafers - which at one time I desperately wanted to taste. LOL
As I grew older, I didn't think much of god or church. It wasn't until I started posting on messageboards and reading discussions on religion that I realized I was no longer a 'Christian.' That realization didn't make me happy or sad. It just... made sense.
The only significant thing that has changed in me that I can think of is how I view my life and the lives of others around me. I guess I'm a bit more selfish, to be honest.
Several years ago, it came to me quite suddenly (although it really shouldn't have been much of a surprise) that this was it. I had one chance at life and this was it. With that realization, I've made several decisions that changed the course of my life.
One such decision, involved my partner at the time. My partner was a severe alcoholic, drug addict, and if anyone knows much about that lifestyle, it comes with a whole host of other problems. I told him I would no longer be a party to either his self-destruction or mine. I was not going to waste the rest of my life worrying about him or wishing I had made other choices. As much as I cared for him (we'd been together 14 years at the time), my life was much too important to me to fling it away on a drunk and drug addict.
Today, I'm happy to say that one realization changed two lives for the better. And it's one I often pass onto others.