A GPS unit can be a superb aid to the pilot and if it is in the right hands then it is a great piece of kit. Don't blast off with a GPS if you have not done some planning. Draw all the lines on your chart and fill in your plog as a back up. Having a RNAV unit is good since you can constantly cross check the GPS data. Basic Nav Aid fixing will do the same job. No matter how many replacement batteries you bring with you for your GPS... things can still go wrong!