BuddyPress Sitewide Notice Widget is a WordPress plugin for BuddyPress enhanced websites by jmdodd.
The BuddyPress default theme provides users with an area in the sidebar for the display and dismissal of sitewide notices. This plugin wraps that code in a widget so that users can easily add that functionality to their own widget-ready sidebar without editing sidebar.php.
Download: http://wordpress.org/extend/plugins/buddypress-sitewide-notice-widget/