>> (and my satnav covers the whole of Europe and I *have* used it to navigate through the entire continent and not had a problem with it)"
> I think you've been lucky. I've had some pretty mad suggestions from both satnavs and google maps.
TomTom has led me onto a "path" where my car got stuck in the mud due to lack of solid ground. Google Maps still connects ways in my home town where there is no connection and 50m height difference. TomTom stubbornly tries to route me through a police-only fenced off entrance onto a motorway. It is not as if "commercial" data were flawless. And an upgrade for Europe map data is 50€! Nahh.
As for routing, I recommend you check out http://map.project-osrm.org/ and test a route ("street housenumber, city"), and drag the markers around and set via markers. OSM data, and beautifully FAST. REAL FAST. :-). And Open Source.
As for postcode searching, I just entered the 5 digits of my German home town into the standard OSM search box and it found it exactly. Same for the Swiss town I currently live in.