I have been trying out the recently released Ovi Maps 3.0.  There are a few nice features that arent in Garmin XT that I like:  

- The super-fast zoom and pan around maps and the ability to then quickly search for a place near the location on the map

- The voice guidance seems to be more detailed with instructions like "at the end of the road ..." and ""turn slightly left ..."  and the way it concatenates directions when you need to make a couple of turns close to each other

- The user interface is much nicer with animations

- The ability to easily preview the whole route and prview each upcoming turn on a route while you are navigating

- Very fast route (re)calculation

On the down side 

- some of the routes it calcs seem a bit unusual

- the NZ maps data is not as current as using Garmin XT with the NZ OpenGPS mapset

- having to pay for ongoing voice guidance license

All up I would have to say that it is a massive improvement over the previous version of Maps and it is now a very usable application.  All I need now is a hybrid combination of the good bits from Garmin combined with the good bits from Ovi Maps wrapped up into one application.