I think it should make a good navigation device with its screen that is much bigger than a TomTom and more convenient and smaller than a laptop (no keyboard). It is going to need an in-car mount to be workable. I also have some concerns about GPS tracking. It does fine when static, but I haven't been able to give it a good driving test.
The inbuilt native Google Maps app seems to work pretty well (again, haven't tried using it for navigating). For other maps, I've tried MapTap (simple map viewer & current location viewer that uses streaming OSM data); and WunderMap (from Wunderground). Wundermap is based on Google Maps but is the best iPad map app I've seen so far, with overlays for temperature, cloud, and precipitation. Cloud & precipitation are animated. The cloud appears to be global (except the polar regions), so you can see things like the volcanic plumefrom Eyjafjallajokull.
Richard