Mac: OS X doesn't come with a lot of options for customising the behaviour of the Notification Center. Fortunately, NCutil is a command line utility that lets you change all sorts of settings.
With NCutil, you can quickly change any apps basic notifications settings using a Terminal command. You can also dig into some deeper settings, including changing alert times, editing multiple alerts at once, remove Apple's App Store specific notifications, and more. If you want a little more control over Notification Center, NCutil is worth a look.