There is a beautiful "Interactive Conference Map" for Google IO 2010 here: http://www.google.com/events/io/2010/map/#level1
Notice the overlays and useful layout. It works well on mobile devices too.
I want to do the same thing, but instead of GMaps loading new tiles every time it is panned or zoomed, I want to have all the tiles pre-cached. This also means it wouldn't need data connection.
Someone told me it was against GMaps Terms of Service to pre-cache the tiles, but have been unable to find out for sure. If it IS against their terms of service, I wonder if there is another way (another service) someone has found, e.g. using OpenStreetMap.