It's sometimes useful to present some information to all users in a semi-persistent fashion, related to the site as a whole. Create a mechanism to store and present these notifications.
The notifications should be semi-persistent, unlike the existing flash messages. The notifications should be closable; once closed, they should not show up for that user again until a new message is in effect. The notifications should also support a (per message?) configurable number of impressions per user; after the user has seen the message the specified number of times, it should no longer be shown to that user.