[noelwelsh]

I disagree. I believe the unidirectional links in the social graph + public by default are the key features.

Because Twitter is public by default I know everything I post should not be confidential. No details of my kids, for instance. So it tends towards people presenting their professional persona.

Because it's unidirectional, following someone does not imply any personal relationship (cf Facebook, where links are bidirectional and you only friends IRL friends). This means I can follow someone without fear of rejection, and likewise I can gain followers without opening myself up to all my followers' content.

With this I can read someone's posts for a while, and comment when I have a feel for them + have something interesting to say.

[dwightgunning]

No doubt they're important factors but I don't think they're the game changer. The blogosphere (with comments + RSS) exhibited those traits long before Twitter arrived.