In the home screen, one can "Save calendar selection" which will add the selection to the "Favorites". Improvements would be "Save as Favorite", "Add to Favorites", "Mark Favorite" ... Observed in 4:4.5~20100930.1181090-1maemo1.1180919 .
This button got removed in revision 1181520.
Confirmed, version 4:4.5~20101014.1185761-1maemo1.1185672 .