Sue & Paul's gMapPedometer is a pretty simple, but slick use of the GoogleMaps API to produce what they call a pedometer. You can 'Start Recording', double-click points on the map and the route is built-up, points added and plotted out and the total distance calculated.
This kind of interface for building a route, perhaps adding some notes, pictures, movie, audio, etc. and then saving the "permalink" for friends and such is great. An easy way to build up a guided tour.