For those of you that work with a lot of 3D objects AutoCAD 2006 has a new system variable that gives you more control over your Object Snaps. Traditionally, object snaps have snapped to the X, Y, and Z coordinate of objects. At times this could be frustrating to users who wanted to create just 2D geometry, if they selected any object that was at its actual elevation, like a contour. They were snapping to that elevation. AutoCAD 2006 gives you control over that behavior with the OSNAPZ system variable. If you type OSNAPZ at the command line and set the value to 1, your object snaps will use the default elevation setting in the drawing, usually zero, for all object snaps. If you set OSNAPZ to 0, your object snaps will use the elevation of the object that you select as it has in the past.
You can also set this variable on the Drafting Tab of the Options dialog box.
If you enable the Replace Z value with current elevation option it will set the OSNAPZ variable to 1.