The UNDO command is surely one of the greatest time-saving inventions of the digital age. According to Jensen Harris, the head honcho of the Microsoft Office User Experience Team, undo is the fourth-most used command in Microsoft Word. (It slots in after Paste, Save and Copy and immediately before Bold.) That popularity is no surprise. Before undo, disaster was a keystroke or a mouse-slip away; with undo, we're protected from many of our blunders.