There are about a dozen people I follow on Twitter whom I’ve never actually met (or whom I’ve met only briefly) but who after months of exchanging tweets I can honestly call good friends.
In other words, we have formed our friendships completely on Twitter, from scratch. This is probably happening to a lot of people, too. Maybe even you (if you use Twitter).
You might follow someone you don’t really know for any number of reasons: You may have seen the person’s name in another friend’s tweet and thought that they sound interesting. You may want to follow a well-known peer. You may have met someone in passing in real life and wished you could hang out more with them, so you search for them on Twitter. You may look at other people’s follow lists and decide that whoever they follow you should follow.
A mutual friend may even make an introduction by simply suggesting “you should follow @johndoe” — which is kind of like saying “you should meet John Doe” except that, because Twitter is basically one-way, the other person isn’t obliged to acknowledge or participate in any formal introduction.
It’s a kind of passive introduction network, where by “following” someone and monitoring their lives (and their conversations with other tweeple) you can get to know them fairly well before actually engaging them in @name public conversations, and eventually in d name direct message conversations.
This probably happens on other social networks, too (for example on Facebook’s walls where you can peek into the conversations of other users and find people you would like to meet), but because most social networks require mutual approval of friendship links, the friend-making dynamic is fraught with a far more emotional and social complexity. Twitter’s fundamental one-way nature lightens the emotional load of making new friends in ways that most other networks just can’t do.