www.hdscs.org has details on one of the best organized ARES groups in the country, with records of their callout history. We work with county disaster agencies and hospitals, and were recently briefed by 3 people who were deployed to Katrina relief - 2 as part of their jobs (1 nurse, 1 Emergency Medical coordinator, one as a Red Cross volunteer).
Lots of good background info on how ham radio can integrate with local agencies to work disasters - but it works best if you work with them BEFORE the disaster, in all of their planning and drills, so they know what hams can do, and the hams know what the served agencies need, and are prepared to provide it.
Fred Wagner, KQ6Q
member of the Hospital Disaster Support Communications System