Simply having tyres that are close to the legal minimum tread depth will increase your speedo readings by a few MPH as you are covering less distance for every rotation of the driveshaft. Car speedos are never accurate and as has already been stated in many parts of the world the law forces or encourages them to overread. Therefore a GPS speedo is a nice thing to have.

While we're at it, can we have an option to make CF set the time and date based on the info it collects from GPS. This will mean that when I restore from hibernation and my date is wrong, it will be fixed, then when Destinator makes CF bomb out and I have to restart it while hurtling down the motorway I don't have to worry about setting the date again.

FWIW I do use my satnav most days. I am a field engineer and I cover most of the UK, and while I know the routes from my house to pretty much all of my customers, when it comes to visiting two sites in one day I basically need satnav. I did 600 miles today and used Destinator to get me to my second and third jobs. It performed admirably, apart from one crash which interestingly was on the exact same bit of road as when I was following the same route on friday. I guess it is just new features in PN that D3 doesn't like.