I didn't notice the feature :-)
We may need a description about keyboard shortcuts somewhere in Info section.
Here is a summary as far as I found:
- 1-9 : Select a move.
- A-Z : Select a move by marker label.
- I : Add the position as (or change the type to) Ideal move (unless marker "I" exists).
- Right : Go forward by 1 move.
- Left : Go back by 1 move (or 10 moves with shift key).
- Up/Down : Vote for/against the position and its type.
- ` : Pass. ('@' key for Japanese arrangement, may also vary for others.)
EDIT: The action of Up/Down has changed.