In OSX you can select an option to start an application at
login as 'hidden' when doing this manually through System
Preferences. I notice that when setting this through AIR's API
there doesn't seem to be this option and it defaults to 'not
hidden'. Not an issue for Windows as when you start an app with no
default window, the app doesn't get focus - whereas on OSX it does
even though there's no window to show.