I am a geography and GIS educator. As I am updating all of my course materials to ArcGIS 10, I am finding numerous little annoyances along the way (plus a couple of major annoyances (go ahead and ask me why I hate the way Esri resdesigned the Spatial Analyst toolbar and Raster Calculator)).
My latest little annoyance is with the Measure tool. In previous versions of ArcGIS, Distance units could be set to both decimal degrees and degrees minutes seconds. While some may not see the practical utility in these two units, I can assure you as a GIS educator, they were invaluable in distilling the concepts of map projections. For instance, I would have students measure the distance between 30° graticules in different parts of the world in both decimal degrees and kilometers to demonstrate that a degree is not a uniform unit of measurement, rather varies based on position of the Earth.
Guess what, can't do that one any more (unless there is a hidden option somewhere I am overlooking). Ugh!!!
(I will commend Esri on the snapping feature in the Measure tool, though. They got that right.)