Actually, this was answered in your [previous question][1] :)

*some private things do go into the inbox. They are quite rare, but they're there.*  
Personally, I've never seen any of those 'private things', but I'm not [user 1][2] either.  
Do admins use it to send ponies to each other?


  [1]: https://stackapps.com/questions/1705/global-inbox-uses-the-api
  [2]: https://stackoverflow.com/users/1/jeff-atwood