https://openflights.org/ uses the Haversine formula (and much more!) to not just compute distance, but plot great circle flight routes on a world map:

https://github.com/jpatokal/openflights/blob/master/js/great...

There are a lot of interesting edge cases regarding routes that cross the dateline, the North Pole, etc. Most of the code was taken from Movable Type's incredible library of lat/long code:

http://www.movable-type.co.uk/scripts/latlong.html