I've held online friendships with dozens of people since i've been using the net as a teen... most i've lost contact with for one reason or another.
Through it all there is only one person who has been there for almost that entire length of time, an older married woman from America I love to death and would consider like a sister to me. We only talk every couple of months or so now, but its always great catching up and our boundaries are very clear with one another (although our conversations did start off very sexual in nature). We've helped each other with a lot of things, and she is a beautiful person.
Otherwise, just posting on forums and special interest chat rooms i've gathered a lot of people I talk to on MSN and facebook regularly who often provide me with entertainment, and the odd confessional where we give each other advice. It is amazing how much you can learn about someone you have never met in person, I don't know if I would quite say we are "friends" in a traditional sense but we certainly have social interaction of a kind. All it would take is bridging that gap by meeting them in person, if you hit it off great if not well, some people probably just aren't comfortable exposing themselves through more confronting means of communication to who they consider their online friends.