The religion issue would be a big deal for me in a relationship. I myself am not religious and I do avoid relationships with people who are. Mostly, because I wouldn't want to be pressured into something I'm not comfortable with. Like wise I would imagine that it would be difficult for someone who is religious to have a partner who is not. This exact issue was one of the main reasons for my parent's divorce. My dad wanted us all to go to church every Sunday and my mom would gripe and complain about going even though she did end up going most of the time. That friction would always lead to an argument later on in the day without fail.