Today, US security forces announced that they would issue security alerts via Facebook and Twitter. Considering the virality of such media, I am sure it would get propagate very quickly. Though that is the purpose of such alerts, the alert would result into a widespread panic and chaos. Hence, the security forced would adapt this as a last resort when all other notification and alerting is done to various administrative and security agencies to be prepared to handle the response.
This launch of alerting on the social media is an example of recent and appropriate usage of socia tech by the government. Other than this, there is another important usage of the Social media that is Social Media Monitoring(SMM).
Social Media monitoring is now very commonly used term in businesses specifically in CRM area by Marketers, Customer Support or Sales force. However, it has usages beyond this class. For example, social scientists and analysts would monitor the media for social trends, social issues as well as impacts of certain events on the society. That is understandable usage. However, more likely that the security forces would also be monitoring the Social medial networks for identifying troubles specifically activities of extremism and terrorism. The security forces already do internet monitoring as in the 2008 report of internet monitoring of terror http://hsgac.senate.gov/public/_files/IslamistReport.pdf. Though this report does not dwelve into the monitoring of Social Media, we can expect that by now, the forces are doing it and able to use the knowledge for detecting and avoiding terror act. However, it may also be intrusing on public privacies.