Funny enough I worked out that the downloaded maps work with Location and not Navigation.
On this phone there is google maps, Navigation and Location.
I tried Location for the first time tonight and it wouldn't re-route when it realised the location it started from was incorrect. Also it wouldnt search by post code and didnt find the village I was looking for by search. Although it did find the village when I searched the street I was going to and I had to go through the entire list. Rubbish
Navigation and Google maps requires data connection.
My impressions of the advertised navigation software (that HTC advertise )is that it is rubbish.
Too be honest, the more I use the phone, the less impressed I get. Has too much rubbish on it and what might be useful just isn't any good.