On Garmin, I like the speed limit notification, I like that fact that I can tell when a turn is coming up more easily; I like that I can touch the top of the screen and see all the upcoming turns. It's also easier to figure out which of several locations recently inputted is the closest to me (helps me as a realtor).
With NAV, sometimes when I try to enter a address or POI it won't let me put all the letters in I need to spell it, because it's decided it doesn't exist! And, maybe I'm missing something, but on the voice activated NAV, I can't input the name of a point of interest--only select from default names either "nearby" or "along the route" (once I've entered in an address). So if the POI IS my destination and it's not nearby, I'm out of luck.
Oh, well, love my 450H (though using the heat and a/c seems to put a serious dent in my gas mileage!).