Microsoft Windows did it right, all notifications are standardized and put into the icon tray. If I want to disable notifications I open the tray settings and disable them there. MacOS never standardized anything, and so every MacOS app creates a new non-standard tray icon, with its own notification system, and some of them now use Growl and some of them don't. It's a mess that even Microsoft managed to standardize 10 years ago.

Microsoft did it exactly right if you assume popup notifications are necessary. I firmly believe that popup notifications are unnecessary and distracting, and that's why I prefer the "notification system" of OS X (red badges in the dock). These are a standard. Growl and menu bar status icons etc are just useless cruft introduced by developers who don't want to adhere to the standard. I could care less if my OS notifies me that it discovered a new input device, or that someone sent me an email labelled "urgent", or whatever.

Of course, OS X is not as clean and notification-free as I'd like it to be: It annoys me every other week or so with some useless software update, and every 10 days it complains that I didn't plug in the backup drive for some time.

Now, it might be possible to configure and disable all these notifications, but I just don't want to bother. I want my computer to act on my command, and in my eyes there is almost no excuse for putting up an unexpected notification or alert or dialog for anything.