When a cyclone ravaged Burma earlier this month, and less than a week later when an earthquake devastated much of China's Sichuan province, some of the first accounts of the disasters were written by bloggers and organizations on Twitter.

Although some live tweets poured in from those in China who were near enough to shoot photos and video, others came from disaster-relief nonprofit organizations.

AmeriCares used Twitter (twitter.com/americares) to disseminate information about its response in Burma, and ...