TR: Some bloggers have complained that Twitter's functionality is limited. Is this simplicity intentional?

EW: Yes. It's very intentional. Simplicity is a really big part of Twitter. As we go forward, we're trying to carefully walk the line between adding functionality and keeping it simple. We know there's lots of functions we want to add and will add, but we also want to wait. We think a lot of the beauty of Twitter is in the simplicity.

Even though it looks like Twitter is just simple text updates, there's a lot going on that's hard to explain. It's a multidevice network that's complicated under the covers. But the only way to make that work is to keep what it does really simple. Because it's so simple, we've seen a lot of our usage come through our API [a platform that lets other people modify Twitter's look and some functions]. It encourages people to play with it and develop tons of different interfaces and tools for it. That couldn't have happened if Twitter were much more complex.

TR: What sorts of tools and interfaces have people developed?

EW: One popular interface is called Twitterific. It's a Mac client that sits on your desktop like an IM window. Your friends' updates will pop up and then fade away like [an] IM. It's a really nice way to use the product if you're on the computer all day, because it gives you this ambient awareness, which you can more or less ignore, of what people are doing.

There are also people taking the [public posts] and doing interesting things with that. The most popular one is called Twitter Vision. It's a world map, and Twitters show up as they're coming in from all over the world. It's very hypnotic.

Also, there are bots [automated computer programs] that are posting as Twitter users based on some information feed. A lot of those are news bots that post headlines. There are others that post the weather, and there are at least two hooked up to the United States Geological Survey that post updates on the location and magnitude of earthquakes.

TR: So Twitter could be used to broadcast important news or emergency announcements?

EW: Yes, and this has broad implications. People have contacted Twitter about [using it as an] emergency broadcast system. We like the idea of it, but we're not anywhere near saying we want to be counted on in emergency situations.

TR: Where is Twitter headed?

EW: Twitter is fairly unique in terms of allowing one to broadcast to many, on a subscription basis, in real time. That's really the heart of Twitter, and what we consider the core. What we're investing in long term is the message router part of it. Messages come in a bunch of different ways, and they all need to go to the right device and the right people. It's all about the message routing and the network and the number of devices that are connected to it.

We'd like to grow the network and the number of people who are using Twitter actively. We are working to extend it so you can send and receive Twitters via e-mail. Also, we're interested in getting more value out of the content that's flowing through the system. We want to allow people to search for users. One of our most requested features is to allow people to form groups. For instance, if people are gathered at an event, it'd be useful to opt in and get Twitters from other people at the event. Likewise, you could have a group for a city such as San Francisco.