In the news.

PBS MediaShift. A better introduction than I can provide.
The Economist:

the medium is hard to dismiss as a reporters’ tool, particularly in countries where cell-phone networks reach farther than the internet. At 4:53 am local time on January 18th Juliana Rotich, a blogger in Kenya, tweeted in her own cablese, “in town nbi.i can smell tear gas in the air”.

The New York Times

What does the crowd look like?
The public timeline. A constant stream of twitters.
Twitter Vision. See where Twitterers are.
Twitterholic. See who is most popular.
Twitterment. Down, for the moment.

Reporting: The new cablese
Twitter-users reported last year’s Mexico City earthquake before the USGS website.
Nate Ritter twittered the San Diego fires.
The Los Angeles Fire Department uses Twitter to post information about emergencies that it is responding to. These messages are then sent to users signed up to receive the information on their mobile devices.
Twitter and Google have produced maps of the primary campaigns, using volunteered information from a network of Twitter-users and news outlets. Here’s the actual map.

Other uses?
Barack Obama has a twitter page, as do many other candidates.
Joshua Rothhaas posts works of original fiction that are exactly 140-characters long.