For years I've toyed with the idea of getting that ideal automotive toy, Sat Nav. A couple of things have always put me off. Price, and price.
First, the price of the Sat Nav unit, and second, the price of the map updates. Both of those impediments have now been removed.
Using a netbook PC, in my case running Ubuntu instead of Windoze, with TangoGPS software, I can utilise maps from many different sources, including Google Maps and Google Earth. Maps from the Open Street Map project are frequently more up to date than anything available as a paid download from the Sat Nav suppliers. Data collected from using this type of GPS system can be uploaded by anyone to keep the maps current.
Considering the number of unidentified roads snaking through the Algarve, using the Google Earth overlays makes finding obscure locations far easier than just using a 2D map - a map which may not even have knowledge of the tracks visible on a satellite image.
The cost? Ubuntu - Free. TangoGPS - Free. Open Street Map & Google Maps - Free. In addition to a netbook PC, the only additional cost is an USB GPS dongle. Cost? €15.
I can just about afford that!