On 8th March from 9:00 to 16:00 some core OpenStreetMap services will be unavailable. Sysadmins will be performing upgrades and testing of the DB server and installing a much faster wiki server.
More information: http://wiki.openstreetmap.org/wiki/March_2013_server_maintenance
Even though the forum itself is not affected, you might be unable to log in during the maintenance because the forum uses OSM user credentials.