Even though running is physically straining, it's mentally refreshing. Especially when you feel like you've accomplished something.

I think we definitely want to focus on the simplicity aspect because it's something that's built into the culture even here at Twitter. Constraints inspire creativity.

With Twitter, it's as easy to unfollow as it is to follow.

You can shut down a service, and yet people will find ways to communicate.

There's a lot of social input when you put these things out there. People's ideas cross with other people's thoughts.

There are a lot of sources of information out there, so why don't you curate for yourself a list, like a real timeline of information, like the New York Times, or JetBlue, or your friends, or this comedian, or this guy who pretends to be a cat, or whatever it is, whatever entertains you, whatever you find useful.

At Twitter, mobile is in our DNA ... For us, it's all about mobile, and it always has been.