AOL recently released the results of a study that identified women over the age of 40 as the most avid players of online games. Over 20 percent of these women developed friendships with others that carried over into offline friendships.
There are many people who believe that the only way real lasting communities can be formed is through regular face to face interaction. In fact, even the William Davies paper that I gushed about expresses this leaning, but it's one that I may not agree with and I think some deeper studies like this one need to be done.
While it's likely that the subjects who met their playing partners in-person ended up having more meaningful friendships, it's quite possible that those who only knew each other through playing each other online were also able to form significant interpersonal relationships. I myself have been a part of numerous online communities and one of the ones that I'm very active in right now is an online gaming clan that's been together for over three years. Many of our members have met face to face, but many haven't, yet there is a very real sense of camaderie between us. Most interestingly, it should be noted that unlike most online communities, we are not a homogenous group of like minds clumped together.
Of all the longer lasting online communities that I've been in, there's been one thing in common. In all of them, a group of people have interacted regularly in a real-time environment. Sometimes it was through regular online chatting, sometimes through online fragging (first person shooter multi-player gaming), and sometimes it was through regular face to face meetings.