So, when someone starts interacting with you out of the blue, you don’t tend to think Who the hell are you? (as it may happen on Twitter). Instead, you feel like you just moved out of the big city, to a smaller town, and you’re surrounded by friendly neighbours who have come here for the same reasons: to escape the urban alienation, so to speak.
I like the analogy between big city and small town. It fits for me because while people are still strangers, strangers in a small town are more aligned with your beliefs and your life than the typical stranger in a big city.
Mori’s post is a great look at why App.net is not the same as Twitter.