Twitter went down last week, and the world got very quiet. People didn't know what do with themselves; they wanted to tweet the news that Twitter was down, but that was out of the question. Entire overheard conversations went unremarked upon, and mini-reviews of recent episodes of True Blood withered on the vine. I saw a funny Onion video that I was sure my followers would have appreciated and an outrageous Rush Limbaugh quote that demanded my impassioned response, but what could I do? Twitter was down for just a few hours—the service's first major outage during its new era of ubiquity—and it felt strange. It's not normal for an entire medium of communication to go offline; sure, sometimes Gmail is balky and your office phones won't respond, but for everyone else, e-mail and the phones and the Web still work. When Twitter goes down, it's down for everyone, everywhere.

Twitter is run by a single company in a single office building in San Francisco. When you send out a message, it flies about Twitter's servers and then alights in all your Twitter pals' cell phones and Tweetdecks. The system is fast and technologically simple, which helps explain its exponential growth.

But for Twitter, centralization is also a curse. In its early days, the site was known for its regular brokenness—its error-page logo, the "fail whale," became a cultural shorthand for suckiness. Twitter went down so often because the idea behind Twitter—sending out short status updates to the world—became too popular for one company to handle.