Thanks for all the new input here...
I don't need all the North America maps at once in the GPS, so I don't need a large SD card.
I don't want to have a pre-programmed SD cards with the maps, since I sometimes uses the maps to locate a coordinates on my computer, and that I want to also have some topos on the cards which, as far as I know, is impossible to do using an SD card.
I live in Canada, and I'm currently using Metroguide Canada v4. However, the maps didn't get an update for some time now (2002), and some streets are outdated, GPS going through lot of turns when it could just have taken a "new" road. That's one of the reasons why I consider CityNav.
One other advantage the NT version has over the non-NT for Canada is the support for postal code, which is only in the NT version. I don't think it's an essential feature, since I rarely need to find a place with a postal code... I guess I'll go with the non-NT version, because I agree that the NT decompression requires a little more processing power that may not be always available on portable units like the 60c' series.
Thanks to all of you!