I have never fostered friendships via social networking sites (because I hate them) and don't view HubPages as an appropriate venue for such things, since it is a writing site and not an AOL chat room.
However, I used to be very heavily involved in online MMORPGs (massively multi-player online role-playing games) and met in "real life" quite a few people that I had befriended in the game realm.
I have "online-turned-real" friends in Quantico (Virginia), Napa (California), Los Angeles (California), St. Louis (Missouri), Portland (Oregon), and Winnepeg (Manitoba, Canada). I have met them all in person.
Two of my online pals (a male and a female) met through a game we played online and eventually got married and have been together for almost ten years.
The only real problem, as I see it, with meeting someone online before meeting them in person is that you have no idea if that person is being genuine with anything they tell you about themselves. An online venue is the perfect place for someone to completely recreate their identity and become the person they've always wanted to be, or become the darker side of themselves that they cannot show to society.