Mapping and GIS remind me of my original profession of civil engineering: nobody notices it when it works.
Mapping is crucial for the clean-up months following disasters. The first time I encountered this was during my time at Cadalyst magazine, when we ran an article about using AutoCAD to map the huge oil spill in Prince William Sound following the Exxon tanker leak. Data was collected from anyone working on the shore or on the waters -- extent of the oil, location of affected animals and birds -- and each day new maps were generated.
Maps were used following 9/11 in New York and the break-up of the Columbia spacecraft. In this week's edition of GIS Monitor, editor Adena Schutzberg describes the mapping resources being made available for the tsunami-affected regions. She also corrects the media's misrepresentation on the use of "secret spy" satellites.
Example of maps here: Sri Lanka Situation Reports and Maps