Not really, could be handy to have different options, but I was just thinking a simple string field that you had the option to display after user logs in. It would be used for messages like;
\"There will be system maintenance this Friday at 10:00 am for one hour, OpenKM will be unavailable during this time.\"
or,
\"The directory structure under Projects has been updated, please take some time to review the new structure.\"
or,
\"Permissions to the Finiance directory have been updated. If you do not have access to this and believe you should please contact the System Administrator.\"
That sort of thing. Just simple messages, that you can pop up once a user logs on, which they read and close, and Administrator has the ability to turn on and off.
Actually, if you wanted to get fancy, you could even have option to display the message to certain groups only.