I have been tracking Twitter use during Hurricane Ike. Several accounts are devoted to assisting or communicating updates during the crisis;
TrackingIke http://www.statesman.com/
hurricaneike http://digg.com/general_sciences/Live_Hurricane_Ike_Coverage_on_Twitter
dw_Ike http://www.disasterwatch.org/
chronhurricane http://www.chron.com/news/specials/hurricane/
This one is of particular note: http://www.ecitizencorps.com/ showing up as "ecert" on Twitter, it's purpose is stated as;
"Uniting New Media Communities for National Preparedness
eCitizen Corps asks you to embrace the personal responsibility to be prepared; to get training in using social networks, blogging and new media; and to use these skills as a eVolunteer to support local emergency responders, disaster relief, and community safety."
One of the leaders of eCitizenCorps was sending messages such as; "US Department of Homeland Security Guard deployed 3500+ officers have come in through EMAC http://www.emacweb.org/ Hurricane Ike #Ike"
The number sign ahead of Ike is a hashtag(a community-driven convention for adding additional context and metadata to your tweets. They're like tags on Flickr, only added inline to your post. You create a hashtag simply by prefixing a word with a hash symbol: #hashtag) developed as a means to create groupings on twitter. See; http://hashtags.org/
In addition, the Red Cross is also on Twitter with an account called "Safe and Well" https://disastersafe.redcross.org/and at http://redcrosschat.org/
Updates and links to services and information made available through Twitter are an effective way to communicate in a crises on a large scale.
