Call me progressive, but I've never owned a SatNav device that hasn't been in / for a mobile phone. Was always on a Windows Mobile, using either built in GPS hardware, or a separate BlueTooth GPS receiver, way back yonder.
Now I've shifted to Sygic Mobile Maps UK on the iPhone - its half the price of TomTom on iPhone and uses the same maps! Navigation has only on occasion thrown me down an odd route, but its no showstopper by any stretch.
Wouldn't touch A-GPS as far as I can throw it, as its pointlessly inaccurate for the last 200 or so metres to your destination, which can be quite a bugger for certain journeys, especially those sites where they're not correctly positioned on Google Maps or something - there are plenty.