Do you actually get geographical data or just map imagery? i.e. once you go offline, can you search for a street address?
This is the key difference of real laptop navigation software like S&T, Autoroute, Delorme, iGuidance vs. the patched-together "download image tiles from Google Maps and view it in your browser" solutions. So I'm wondering if this is any different.
From
http://earth.google.com , this is not listed as an additional feature of the $20 Google Earth Plus, as opposed to the free Google Earth.