More recently I stumbled across a program called Twinkle for the iPhone, which is a Twitter client that stores geoloc information with each tweet (Twitter post). You can then do 'Near Me' and see people in your physical area who are Twittering. This creates an instant ad-hoc social network based on location; while in Seattle, the 'Near Me' tab of Twinkle shows other Seattle-area Twitterers, and while I was in Vancouver over the weekend, I saw Vancouver folks.
This suddenly makes Twitter much more interesting to me. I've already stumbled across several other folks and begun chatting this way; it restores a 'local' element to the social networks, and also gives you the 'random encounter' aspect of meeting someone on the street since you can see a public timeline of just local Twitterers. This has also led to a game among some folks, Twinkle-sniping; if someone posts a picture of where they are, and you see a '0 mi.' distance marker, you can try to track them down and take a picture of them.
One of the local Twinkle users has become my self-appointed nemesis, amusingly. This began when he took a picture of the Starbucks near his work and I recognized it as the one a few blocks from me. After I mentioned this, the next day he commented 'im in ur starbucks drinkin all ur coffeez' -- and then, when being told I usually visit Peets and drink tea, remarked, 'Curses! Foiled again!'
Since then, it's become an amusing game as we foil and thwart each other periodically over Twitter. (He wins so far, by going to the JoCo concert in Seattle while I was in Vancouver. Nooo! I missed Jonathon Coulton!) And despite working about three blocks away from each other and going to many of the same places for lunch, we'd never have encountered each other without this sort of ad-hoc social network that Twinkle represents.
I'm beginning to think that despite the global-community benefits of the Internet, there's something to be said for using those tools to reconnect within your own local communities.
Anyway, just some random thoughts. :)