A few years ago I had the pleasure of spending some time with Biz Stone, one of the founders of Twitter. In 2007 his biggest concern appeared to be hardware: “How can we keep on growing like this when everytime we plug in another machine the website is down?”

Few years later it’s amazing to see how fast the website has grown and how little downtime their is nowadays. A series of smart moves (among them: buying summize.com instead of building their own search application) later, Twitter seems to have shifted from “What are you doing” to “What’s happening”.

My guess is that this is the result of Twitter becoming mainstream. It used to be a tool for modern -look at me-marketeers, but it’s becoming more and more a tool for civil reporting. Thus, the question: “what’s happening?” can be easily answered -in realtime- on Twitter.

That’s why I like to state that Twitter became mainstream on 9 December 2009, the moment they changed from What Are You Doing to What’s Happening.

When I was at TED earlier this year in Long Beach, the other founder (Evan Willliams) gave this presentation. Which eventually lead to even Chris Anderson becoming a heavy twitter-user!