This weekends Wainuiomata website development included adding support for GeoDjango and installing PostGIS on the servers so that we can enter coordinates for each location. We've just rolled it out, although it won't be showing yet as we have lots of locations to enter now.
We still want to look at using OpenStreetMap on the main site as it shows we are all about open source. But for the time being it's still using Google Maps in the admin because of the location lookups.
It would be nice to use NZ Post APIs if possible for location lookup to coordinates, if it can do that. But things like that will take time to develop, right now the library we're using already supports Google Maps for location lookups (or MapBox).