Did you ever notice that if you hold down the Shift key too long the ORTHO mode changes to the opposite of what the current setting is?  Yes, that right, you can hold down the Shift key while in a command and change the ORTHO setting temporarily.

A classic example of when to use this great function is when you have ORTHO turned on and need to move a selection set in a non-ortho direction and then go back to using commands with ORTHO on. 

A small graphic symbol will also appear at the cursor crosshair intersection when you are using this trick to let you know visually if you are holding down the Shift key.