Here are the docs
http://code.google.com/apis/maps/documentation/javascript/overlays.html#user_editable_shapes_events
You might need to force the english language version, sometimes
documentation lags behind in other languages
"Polygon editing events
insert_at
remove_at
set_at
The listener must be set on the polygon's path. If the polygon has
multiple paths, a listener must be set on each path."