It is used by a large number of geocaching websites as a format to send cache information.
GPX 1.0 was released in 2002.
GPX 1.1 was released on August 9, 2004. This is the most current version.
GPX enjoys a wide range of support.
- Windows, PDA and Phone Software
This is a very limited list. For a larger but still incomplete list see http://www.topografix.com/gpx_resources.asp.