Twitter works like people do. If I’m interested in someone, I don’t have to ask their permission to follow them. I don’t have to ask if they will be my friend: that is something that evolves naturally over time. If you’re a public figure like I am, the metaphor of mutual “friending” is truly broken. I get tens of thousands of friend requests from people I don’t know. Accepting would make it impossible for me to use a social tool to keep in touch with my real friends."

— Why I Love Twitter - O’Reilly Radar