[mecreyes]

I use iGo 2006 plus. I find the interface, POI and the ability to use it out of your service area as the prime reasons for having installed nav software.
I live in Canada, and with our HUGE country and TINY population, there are large areas that are not serviced digitally. What if there is a power outage? Cell towers are affected by that.
I'm told that iGo is best for Europe, but I find that the maps for North America are extremely detailed street-wise and POI-wise.
If you are worried about space you only need to install the maps you need. All of Canada is roughly 112mb. In the US, its broken down by state which vary depending on the level of inhabited/developed area. I think New York state runs roughly 50mb.
My career revolves around geography/GIS/GPS and decision support. While the Mogul GPS is nowhere close to a Trimble per se, it is a damn good general purpose alternative. I also use ArcPAD 7.1 and find that I have less to carry in the field.
The costs seem to be equal in the US, but the option of being self reliant is much more appealing.