Sandy,
Thanks for sending Solstice along. It looks good. I also enjoyed your comment on Thiessen polygons. I also looked at Barmore (Vol IV, 1, 1993) on ellipsoids. One additional discrepancy between a sphere and ellipsoid is nicely described in Charles Arden-Close's book "Geographical Byways...". This is that the concept of antipodal point must be modified - it can be generalized in several ways, all of which coincide in the case of a sphere.
Waldo