I'd like to point out what seem to be some bugs in Blender.
1. Texture filtering doesn't work on image maps that are applied to the "World."
2. It is correct to have image maps that stretch on the zeniths of the world (top and bottom) but they also appear to be stretching on ONE of the sides of the world, which doesn't really make too much sense to me.
For #2, cubic mapping for the world would probably fix this. I'd like to add this as a feature request.
Thanks! Feedback appreciated.