The F8 key has been used for years to turn ORTHO on or off. The option to pick ORTHO on the status line below the drawing area has always been available as well. Now with AutoCAD 2006, holding down on the SHIFT key will give you instance ORTHO. This will give you ORTHO for the duration that the SHIFT key is held down. This works if ORTHO is turned on or off. Even if POLAR is being used, this handy shortcut will work.
Autodesk has finally started listening to the end users to make designing and drafting with AutoCAD simpler and faster.