The Calendar menu needs a left pane to show all of the user's calendars. This would make it easier to select which calendars to show on the right.
Consistency is important in UI. Currently all the nav bar items (Email, Notes, RSS, File Storage, etc.) have a left pane for organization, but not Calendars.
Using a left pane to show multiple calendars is how Gmail and most clients (Thunderbird, eM Client, etc.) do it. And it would allow ST to move a lot of the functionality that is inconveniently found under Settings (e.g. Add/Delete calendar) directly to the Calendar section. You should be able to create a new calendar just like creating a new folder (Actions -> New Calendar) and not have to go into Settings.