I find that, for the most part, Nokia Drive is pretty good.
When I was in school I did delivery driving for Boston Pizza. I used the provided garmin for that and found that, in Kitchener/Waterloo Ontario, the Nokia Drive functions equally to, and better, than Garmin's did.
Now the Garmin maps were at least 2 years old, so the problems occurred when there were new subdivisions etc. But Nokia maps are pretty damn accurate in this area.
I went to Italy in May of this year and took my 900 with me, got a vodafone sim, and used Nokia drive in Rome, Florence, Naples, and Nokia Maps in Venice (no drivable roads there really....though I should have tried it to see if it even worked there... missed opportunity!). Nokia Drive saved our asses in much of the small towns in the mountains of the Florence area. It even had the tiny town of Donnini and all its little roads. The addresses were almost dead on.
I do, however, have three major gripes with it currently.
1. No custom routing preferences. ie. No way to make it not choose Toll routes. This is a pain in the *** when I drive to Oakville because it always wants to force me to take the 407 Express Toll Route. I want to be able to set it to not take Toll routes, set it to avoid major highways, etc.
2. I get the occasional hiccup in how it identifies routes.
Two examples: near my home, there is a standard intersection but the crossing road enters slightly offset. Barely 10 feet offset. Nokia Drive treats this as a T-intersection. So when you approach from the offset road, it says, turn left, then immediately turn right, and follow the course of the road. In reality, there is no need to turn at all.
Second example, when driving on the MacDonald Carter Freeway to the 401, it tries to make me take the exit at Maple Groove, then immediately puts me back on the Freeway....No point to that at all.
So these are minor bugs, annoying bugs. I expect these sorts of bugs in all routing software though.
3. Where the **** is my My Commute and traffic integration!? I've been trying to find some sort of info when it is coming to Canada but there is no information.