Only issue I had is when I dated a girl and later found out she was pretty religious. As in, when she finally got accepted into Loyola, she said it was God's doing and without God and prayer she wouldn't have been accepted.
Overall, it was fine, we acknowledged our difference in beliefs and were fine with it. However, I will admit it was a factor in why I broke up with her.
For short-term dating, there's no reason to put that much weight on if your religious beliefs match, but for long relationships it can be a bit of an issue. Mainly, I found myself having to catch myself before making comments and that sort of thing. It kind of created subjects and such that I basically kept as "off limits" in my mind simply to avoid arguing, and our views differed a lot on things. Also, there was the physical part where, as I said, she was very Christian and was not open at all to anything past making out. That and it got kind of annoying constantly seeing bible quotes on her facebook status.
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*Lives in the Future*