I bought a portable GPS for our trip in Italy and France.  The unit I got was the Nuvi 360. It can be used in a car, walking or on a bicycle and gives the appropriate directions for the type of transportation used.  I bought a special memory card that has European information in it. Since I have no other experience with a portable unit, I can not recommend this unit versus another.  I tested the unit  in San Francisco where I live and it did great.  It did ok in London but not as well in Italy especially where we are staying in Tuscany with all the small roads and hill towns.  The unit has a computer generated voice.  That works ok with the words are in English but it is horrible and almost unusable when the street names and towns are in Italian.  We switch the language it used to Italian and that works better for us because we understand enough Italian to recognize the directions but otherwise that would be useless too. Two bad the unit does not use English for the directions and Italian for the names of streets and towns.  It should be possible to design it to work that way. But using a GPS that you can carry around in your pocket is a real different experience than a GPS that is in your car.  It is like caring a cell phone when before we had phones mounted in our cars that could not be taken out (if you are old enough to remember that).  The unit can calculate your average speed when you are walking and know if you have stopped somewhere (lets say for lunch) and does not count that time in figuring out your average speed. So I began to think of how a person GPS could be used to enhance one’s own knowledge of one’s behavior.  As I understand it, a GPS can know where I am located within ten feet or so and that will improve in the future to maybe three feet.  So it seems that I could map out my home and provide enough info so that with a GPS that collected and stored and uploaded info (they do this now for bike riders) I could tell where I spent my time in my own home, how long I was at the gym, where I went for lunch etc. Most of us have a GPS with us these days any way. It is called a cell phone.  And there are already applications that can tell me not only where restaurants and book stores are relative to my location but even if I have friends close by.   Soon (or maybe it has already happened) this might be used for dating purposes.  You could be told that a person of interest is close by. 

By the way, now that there are companies that track traffic by following cell phones (they pick out people and follow them to get their speeds), they will also find out the short cuts that worked (worked because once they are found out they may no longer be short cuts). Welcome to village earth.  Enjoy it while it lasts!