In the "How do I" sample project, there is a project "Determine where the user clicked in world coordinate". You can see more tricks related to spatial references on the map in a project in our Code Community.
You can see in the project "Latitude Longitude Coordinate" code.thinkgeo.com/projects/show/graticule some techniques to offer more spatial clues to the user navigating the map. We show how to display lines of latitudes (parallels) and lines of longitude (meridians).