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Twitter has 105 million registered users, with 300,000 new users signing up every day, Stone said, opening Twitter's Chirp conference at the Palace of Fine Arts before an audience just shy of 1,000 developers. That user figure is more than a recent estimate from comScore, which pegged Twitter's user base at 65 million.

The Twitter API (application programming interface) fields 3 billion requests per day, Williams said. "That's bigger than all but a couple of Web sites in the world," he said, claiming it makes Twitter "about the same size as Yahoo." He said the service has grown 1,500% each year on average since "Twitter Inc." was founded three years ago this month. The service is also fielding about 19 billion searches a month, Williams said, which compares to about 90 billion for Google.

But the growth has brought challenges. Twitter has struggled to keep up with the demands on its infrastructure, and Williams acknowledged the past two years have been a chaotic and not always pleasant time for the company.

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More in Web 2.0 His message for developers was that Twitter is putting the difficult times behind it and can now offer a stable, reliable platform on which developers can build new applications.

"Even just in the past few months, Twitter is a qualitatively different company than it has been," Williams said. "We're out of the chaos to some degree, we're reacting better, we've built the infrastructure we need.

"What it means for you guys," he told developers, "is a more stable and organized platform for you to build on."

He addressed the fact that Twitter has started releasing some of its own applications, putting it in competition with its developer community. Referring to the BlackBerry and iPhone applications the company recently released, Williams said he knew it was a "controversial decision" but that it had to be done.

"When we did the research we found we were underserving users," he said. "We had to have a core experience on these platforms just like we have on the Web. We were failing the ecosystem because we were not getting as many people as we could engaged."

The company has seen 100,000 new users sign up through the BlackBerry app in just a few days, and 1.7 percent of all Twitter posts come through the BlackBerry application, he said.

Making Twitter easier to use remains a key objective. "Twitter is too hard to use. It's amazing it has grown as big as it is given how hard it is to use," Williams said.