When I went back to Liverpool, I found out that an up-to-date sat nav device is an essential part of modern living. However like any large database of information there are often inconsistencies that throw up unexpected or wrong results. My Dad told me of a colleague that was sent down a green trail by his sat nav system on his way to find a campsite. A much more common error in the UK is a mistake mapping a postcode to a location.
For instance the RAF Museum in Colindale, North London warns about this on its website. This presents us witih a modern-day conundrum. Since there are only a few map providers, you generally know pretty fast if people cannot find you via their sat nav system. So there is a social etiquette requirement to notify anybody that you maybe inviting over.
On the flipside it would be good form to print out a map of the destination locality from Google Maps before your trip and phone ahead letting your host know if you will be late due to sat nav problems.