Having been one of a handful of drivers who have successfully navigated from London to St. Jean d'Aulps (ie. an obscure place in the Alps), I have nothing but respect for the TomTom GPS receiver. We borrowed one with an extra memory card and European maps. Jane, as she's apparently called directed us flawlessly all the way there and back (some 1500 miles), with daily stops in various random skiing places.
TomToms? are pretty expensive, but I'd imagine invaluable if you need to drive places with any sort of frequency. It does have the slight side effect that you get very dependent very quickly, and don't really read road signs, or make notes of landmarks.