Google has launched so many useful GIS tools in the last years, we should make more use of them.
We are already using their Geocoder. That plug-in needs to be enhanced to save the geocoded addresses so it doesn't need to get the same address from Google over and over again.
Google also has routing abilities, some API for elevation and places:
No doubt Google will add more services in the near future.
Their tiles service will be handled by the new GMap implementation (http://mapwindow4.codeplex.com/discussions/277943) and is beyond the scope of this discussion.