Mine is over 250 meg. I have 4 continents worth of maps/landsat in it. Since it stores the tiles from everywhere you have been, that is understandable. I think if you lost it you would have to re-download when you bring up the various maps. Your GPX files are separate, so you would not loose the actual data you ave collected in the form of GPS tracks. I don't backup my program files directory, which is where the maps1.dat resides, (mine is actually maps0.dat - not sure why), since this information is recoverable off the internet. My GPX files are kept in a directory I do back up.
Brian