Imma jump on the bandwagon. I used to believe in this silly little thing called Christianity until.............. nah, sorry, can't do it. My faith in God has only gotten stronger as I've matured, and it has helped me develop into the loving individual that I am today. But as I've grown up I've dispensed of the overly simplistic viewpoint of God as some old dude riding up on a cloud in the sky, so I guess that counts.
Onto other matters, hmm... I used to believe that once I fell asleep I had to keep my eyes closed and not move a muscle otherwise monsters would see I'm awake and get me. I also believed that, whenever I was in car rides, I had to breathe at certain spots on the road (specifically, at 90-degree and 45-degree angles from the electric poles. Don't ask, I was a weird kid.) I also believed that my Christmas tree angel was possessed (actually that hasn't been disproven so technically I STILL believe that). Oh yeah, and I also believed that my teachers either lived at school or stopped existing when school was out, but then I ran across my favorite elementary teacher in the supermarket and that idea stopped dead in its track.