On Tuesday 20th of March 2012 between 13:45 and 16:15 (GMT / UTC) the
primary database server will unavailable due to emergency maintenance.
The following services will be affected:
- www.openstreetmap.org web site will not allow user login or edits (Potlatch). 
- API and map database editing (using JOSM, Merkaartor etc.) will be unavailable.
- planet.openstreetmap.org will be available but no new diffs will be generated during the outage.
- Forum (no logins)
- trac (bug-tracker, no logins)
- help.openstreetmap.org (no logins)
Other services will not be affected – all of the following are
expected to function normally:
- tile serving (“View The Map” & “Export”)
- Nominatim (search)
- mailing lists
- subversion and git (source code repositories)
Technical: Database Server Smaug: Replacing faulty motherboard.
Supplier Engineer Onsite. We have contingency hardware available.
1: Maps will still be viewable on the openstreetmap.org homepage and
on other people’s websites.
On behalf of the OpenStreetMap sysadmin team
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All my openstreetmap maps have stopped working. eg http://www.carnethy.com/maps/wed_training/wed_training_29-feb-12.htm
Is this because of the downtime?
Answer found here:
Osmarender has shut down and if a layer declaration is left in it buggers the map.
Downtime is co-incidental