I am having a lot of fun with competition Opera is currently running – matching daily photo to country. Was laughing about how it took me seconds to determine place several countries away but a lot of time for place that is only few streets far.
What it does
Most of site is regular Google map with all features of such like dynamic scaling and multiply display modes.
Site adds to it two markers and tells you distance between them in kilometers and miles. You can change positions by typing places in or simply moving markers them on the map.
Honestly I doubt such information is very practical. Still I needed it, site’s developer needed it and since site is still live there are enough people visiting who do need it as well.
Simple but well-implemented mashup that does its thing well.