LoadMyTracks is a piece of software that will communicate with GPS devices from many manufacturers to send and receive data. It can also be used to translate data between the popular GPX and KML (Google Earth) formats. The software provides support for Waypoints (single locations in space), Routes (lists of waypoints that can be used as instructions of where to go, Tracks (the breadcrumbs that many GPS devices keep to show where you have been) and additional data that may vary by device.
With GPX files, you can log your travels, determine the location of your photos on your latest photo safari, plan and track exercise, participate in geocaching, help make better maps of your country's roadways, or anything that your geospatial mind can think of. Utilities exist on the Internet and on the Macintosh to use and manipulate GPX files. Google is a great place to start when trying to find these.