David Mear, who worked on the Moon Zoo flash interface told us about these keyboard shortcuts:
Cursor keys: Nudge the selected annotation.
Shift + cursor keys: Nudge the annotation by ten pixels at a time.
Backspace: Delete the selected annotation.
C: Toggle the crater tool.
A: Toggle the area tool.
H: Show or hide the selected annotation.
Shift + H: Show or hide all.
1, 2 and 3: Set the selected crater's boulderyness to "None", "Some" or "Many".
Ctrl + Z: Undo
Ctrl + Shift + Z or Ctrl + Y: Redo
Tab cycles through the tool buttons