I started with two questions but ended up with more...
Do you actually have to be "doing" navigation for it use the satnav data, or does it keep track of where you are all the time anyway?
If a speed limit sign overrides the satnav data (e.g. for temporary roadworks) then will the system recognise the sign and show you the lower limit?
Given the speed limit recognition, can that feed into the cruise control system and slow you down when, say, a dual carriageway becomes a single carriageway with a lower limit?
Finally, given we have a camera that can recognise speed limit signs, I wonder if it could (in future) recognise traffic lights and warn you if you were about to cross a red one? Just speculating now...
Sorry for all the questions... I promise that when I have a car I'll spend time providing answers