This one definitely gets filed under the “I did not know that” category (a fairly substantial category as you might imagine). Apparently for a few years now the USGS has hosted volunteers through The National Map Corps. By volunteering you receive an area (quad sheet or less) in which you and your trusty GPS unit go out and gather information on commonly mapped features (churches, schools, communications) and send in the information to be included in the National Map. After you have completed the initial data acquisition you are also supposed to send in changes over time (demolition, name change, etc) to help keep the National Map up-to-date. A cool idea that has been echoed more recently in TomTom’s Mapshare and of course the more ambitious OSM. If you like to spend time with your GPS unit you should look into the TNMC.