I liked the Growl notification customizations on the Mac, where every possible notification type for an app was listed. That’s how it should be; then you know everything that the app can possibly send. You could make broad preferences where desired, and granular settings as needed.

I hate that installing new apps enables every stupid notification by default, seemingly only fixable by going 3 levels deep into every app’s settings and disabling things. Designers talk about the importance of having good defaults, and notifications have really, really stupid defaults coupled with bad UI for fixing them.