Ooohh sure, I have also heard of such stories. For me I tried dating my childhood friend immediately after high school. Surprisingly, the relationship never lasted even three months. We were so much used to each other and even that aspect of respect was never there. We still saw each other just as a friend. After some time we both agreed that each one should go their away because things could never work out for us. Still after breaking up, we were both cheerful and kept of talking to each other, I mean there was no grudge between us.
It will not be easy dating someone you've seen since your childhood and knows almost everything about you. As for those who have succeeded with those kind of relationships, I can say its just luck and they were truly meant for each other.