I use Navicore a lot here in the Middle East on my Nokia N80i and it works real well.
Back in the states I used TomTom on the same N80i and it worked well too.

Navicore make core navigation software products that OTHER navigation companies wind up using in their own "branded" solutions.
Looking at the official Nokia GPS receiver I see that it's actually BIGGER than my Holux GPSlim 240.
I'm going to wait a little while and probably wind up buying just the NA software for it. But I'm kind of partial to using offline maps with Maemo Mapper on the N800 to map out my properties mostly due to the satellite maps.