BBC prog; the Museum of Curiosity A factual comedy show.
In it, former director of the Greenwich Observatory Dr Kristin Lippincott, pointed out that due to the Earth's wobble & slowing down, they have to alter GMT by leap seconds just to make the GPS come back to Greenwich at the observatory.

The zero meridian is not as important, but it means all SatNavs will be out by as much as 100 metres, one second before the leap second kicks in. Which is a somewhat variable occurrence, for the general public at least. Unless you have a really swanky SatNav that is in communication with a phone network and is designed to compensate. (I know of none such, but haven't investigated)

Of course if you don't set the SatNav to roads (fastest or shortest) it may send you down a footpath. 100 metres would be damn close in that scenario!