Notifications, one of the new features of Mavericks, allows you to group all alerts from applications such as mail, messages, plans, skype, safari and many others. Although very practical, notifications can be annoying and distracting. Learn how to temporarily disable them with a single click.
To do this, simply click on the icon Notifications while keeping the touch Pressed options (ALT key).
This has the effect of greying the icon Notifications and disable all notifications displayed as banners and/or alerts (mail, calendar, facetime, messages, game center, reminders, safari, twitter...).
Note that they will be automatically reactivated the day after deactivation.
A hidden option but easy to access very practical especially in the case of a Keynote/PowerPoint presentation or when viewing a film.