Unless I have missed a big important feature, I wish I could always snap to the orthogonal extremes of these shapes without need for construction lines. Ideally these positions would be keypoints which can be made visible in display options like existing keypoints. Ideally we could also set the number of increments for a circle or smooth circular object. I would like circular derived 3d objects and parts of objects to also maintain these keypoints for snapping to until the circular or elipitical nature of the shape is lost. With elipse this would ideally be with a choice for equal angle increment or equal interval of segment length.
At the moment, if a circle produced starting from centre, if care is taken to construct the circle in an orthogonal direction, lets say for example sideways, one side is snap-able with vertex snap, and the other with interval snap.
Other Cad software has this and is useful very frequently. With Turbocad, which I used to use, after rotating, depending on the settings, also offered /offers the 2d and 3d object coordinate system for selected objects to either be maintained, or refreshed to align with world coordinates.
I hope we see this improvement in version 9.