I am an avid mountain biker and spent a considerable portion of the Thanksgiving break riding local trails. My fellow Googler and cyclist Dave joined me and brought his nifty Garmin GPSMAP 60CSx GPS device with him to track our trail riding.
Google Earth Pro and Plus allow you to import GPS data and display it in the 3D viewer. As someone who has used electronic maps for many years, I love this feature. You can see exactly where you rode and with terrain turned on, you can gain new perspective on your trek. Often, I view the GPS track of a ride and think "ahhhh... so that is why my legs hurt so much. That hill is steep!"
Other website designers have come up with innovative ways to display GPS data in Google Earth and Google Maps. One such site is mtbguru.com which makes very effective use of GPS and KML. It even displays geo-referenced photographs taken on the trails. MotionBased is another great web-based service that allows you to review GPS data and view it in Google Earth and Maps.