The Twitter blog explains their thinking behind changing the foundational question from “What are you doing?” to “What’s happening?”
The fundamentally open model of Twitter created a new kind of information network and it has long outgrown the concept of personal status updates. Twitter helps you share and discover what’s happening now among all the things, people, and events you care about. “What are you doing?” isn’t the right question anymore—starting today, we’ve shortened it by two characters. Twitter now asks, “What’s happening?”
If you’re a tweeter, have you used Twitter solely to express your personal status throughout the day, or is Twitter for you more of a give-and-take about what’s on your mind and on the minds of those who reply and retweet? It’s a very different social experience depending on which approach you take.