When you set an assignment's letter grade scale to Letter grades and you try to enter in grades in the gradebook a pop-up window pops up with the grades available that you can select.  This is nice for when you need to enter in 1 or 2 grades, but if you need to enter in a lot of grades it is really inefficient.  You should allow teachers to enter in letter grades via the keyboard.  Another improvement would be to allow you to clear the grades window by pressing the Esc key on the keyboard.