This is based on the comments on Caleb's answer, rather than the original question, but still somewhat applies to the original question.
I agree completely with Caleb's answer, but would add this:
Ideally, you'd want to marry someone who has the same beliefs as you, and someone who's close to where you are on the scale of spiritual vs. carnal.
I thank God every day that I did this. I have close personal friends that have a lot of stress in their households that I don't have to deal with simply because of a discrepancy between husband and wife on what they believe to be truth.
It's hard enough for, say, a Baptist to be married to a Catholic - or a Lutheran to marry a LDS member - or a Young-Earth Creationist (denomination not important) married to a Secular Humanist. There are enough doctrinal differences between some of the denominations - things that each denomination teaches/views differently - that it can be a real contention point. Arguments over how we are to live our day-to-day lives are more likely. Our actions and worldview is so intricately tied with how we see God that it's simply inevitable.
Once kids enter the picture, it's a whole new ball game. Who gets to teach the kids what? And if one spouse thinks the other is leading the kids into error, and possibly Hell, that's simply a no-win situation.
The other thing I've seen that has torn marriages apart is when one spouse is very faithful, very spiritual, and the other is more worldly. One tends to think the other is a religious nut-job, while the other things their partner is either not saved in the first place, or just not living the way he/she should. Even with the same basic doctrinal beliefs, a discrepancy in how strongly those beliefs affect day-to-day living can cause issues.
Being equally yoked is very good advice. Being unequally yoked is simply not a recipe for a harmonious home.