Most of the people I know find sex and relationship partners among their friends and acquaintances. As far as I can see with is the case for my friends in Helsinki, my childhood friends in Boston, my parents' childhood friends in St. Petersburg, and my grandparents. (Although I do know some people who have found their partners as strangers in the bars or on some Net dating service, and they seem happy enough.)
However, the people claiming that once a man is friends with a woman he has no chance are so numerous, that probably somewhere out there there must be a place (geographical or social) where this is in fact the case. I am just curious: where is it?