From NSAlert documentation:
Currently, there is no visual difference between informational and warning alerts.
This was written at the time of Panther and this is still true in Snow Leopard. So why the hell is the setAlertStyle: method provided?
NSCriticalAlertStyleThis style causes the icon to be badged with a caution icon.
A caution icon, for a critical alert? That does not make sense!
Here are screenshots of the default behaviours with the three different alert styles:
The documentation is unfortunately right: there is no difference between the informational and the warning style. The critical style is indeed badged with a caution icon.
As you probably have guessed from the title of this post, I am not happy with this behavior, so I have written a class, CLAlert (MIT License) that displays alerts the way I think it should be done. I.e. a note icon for an informational alert, a caution icon for a warning alert and a stop icon for a critical alert as you can see on these screenshots.
CLAlert is a drop-in replacement for NSAlert. It requires at lest Mac OS X 10.5.