I have made a spreadsheet to calculate distances on the World Map. Put in the from and to co-ordinates in the grey cells and the distance is displayed. Note that it doesn't take into account obstacles.https://docs.google.com/spreadsheet/ccc?key=0AgiblAFn-XSkdEI4Ymk4aHRMQ3BRVUpKQzZFZkVTLUE
For those who are interested, what it does is slant the wriggley y-axis at 120 degrees to the x-axis then adds a third z-axis at 120 dgrees to the other two. Distance is the maximum absolute of the three deltas.
Let me know what you think!