I was in Helen's car (a 2002 Prius) the other day and we used the GPS to get from one place to another.
The UI for entering the destination address was pretty awesome! When you push letters, letters that couldn't happen after disappear. So if I type 'S-o-u', every letter but 't' dims. Ok, so clever use of a trie. But they filled the trie with the street names in the US - so once I type in 's-o-u-t-h-b-r', very few letters are up - it's not trying to build a compound word, but it really only looks at legit street names.
Once you enter the street name, they show you only cities that have streets of that name in the state (I forget how one chooses another state).
I have to say, they could have put a pretty bad UI in the system - one where you enter every little detail - but they seemed to take the extra step and make it that much better. (My only complaint: they do an ABCDEF keyboard instead of QWERTY)
I'm glad I never played with this system before I bought my new car. Otherwise I might have tried to hold out for a GPS system!