Japanese car navigation systems (navi systems) are awesome. Every country I visit, I ask the question about what the navigation system covers and it seems Japan still has the edge on most. Finding your destination by address, phone number, general location etc has been around for a long time but how about McDonalds or fuel or hotels (of various kinds) or police road blocks. They even give you the heads up on speed traps. However, for me, the really impressive feature of the Japanese system is the real time traffic information on almost all roads across the country. I'm not talking simply highways but in-city roads too and the re-routing system is seamless and simple.
There is really only one problem for the newcomer to Japan and that's that the maps are, and will always probably remain, in Japanese. Menus can often be switched between English and Japanese but the incentive for the manufacturer to invest in creating an English map is virtually zero. Navi systems have taken the tension out of a marriage on a long journey when a map book used to be involved and will be able to show you the traffic ahead if nothing else but you may need the support of Google Maps to really get around. Next step, learning kanji.