Learning a bit more about about these devices will let you appreciate far more what they can do for you.  remember that even though they rely on the same basic operation not all devices are created equal.. Some work faster and many have different features that you'll want to investigate.

GPS navigation systems use a set of 24 satellites to provide coverage over the globe and for any gps device to pinpoint its location it must receive signals from at least 3 satellites.  Each satellite has a unique identifier code and sofware in the GPS unit can work out the exact location of each satellite i.e. where it expects the satellite to be.  By measuring the time it takes for the signal transmission from the satellte to reach the GPS device and measuring 3 such signals an exact location on the surface of the earth can be calculated.  Often data from a fourth satellite is also measured to ensure accuracy.

GPS navigation systems are far more sophisticated than the original military systems that gave “only” an accurate position.  These days as well as the position a GPS navigator will let you enter your route with way points and will make up for any detours that you accidentaly make and get you back on track.  Many systems also offer an upgrade package (or subscription) that will give you up to the minute traffic situations, weather and road works along your path.  Of course the cost may be a deterent to a casual driver but theres services will prove invaluable to people travelling to work where they must not be late.

Remember to ensure you buy a system that can be easily upgraded either by CD or memory card so you can obtain up to date maps to get the best usage from your GPS navigation systems since new roads are always being created and old ones closed.  This will make sure you get the longest use from your GPS system.