I donīt have a GPS device (yet). But if I had one I would stop say every 30 minutes or 1 hour and write down the position readout on the piece of paper along with actual time. If the GPS dies on you later on, you can estimate from this data your current position and plot it on the map. (It doesnīt mean I wouldnīt navigate myself using a map. But with written down coordinates from GPS estimating your position might be more precise).

It comes in handy especially for those people that use mainly GPS and map + compass is just their backup (as long as they know how to plot coordinates from GPS on a paper map and have the tools for the job).

Just an idea.